Yes. Cut her off. Disengage. You are being used by an ungrateful little poo head. She has 2 parents who need to be providing for her.

Yes you are. But no worries we have all been that "idiot" as you put it. Obviously doing kind things for someone and getting little or nothing in gratitude is humiliating and hurtful. Until she improves her attitude I would treat her the same.
Sounds like daddy is half heartedly putting her in her place, that is why she continues. Because she can.
Ignore the brat.

If she cut you out of her life, then you should let your SO deal with all of her requests. I'm honestly more mad at him for letting her get away with that.

She's using you. You don't have to tell her that you're not going to help her anymore, just be "unavailable" when she wants to talk to you.

Also, if you could, I would screenshot the things she said about stepparents, just for your own records, in case you need to remind people who cut whom off.

She honestly sounds like a terrible person and your SO should be sort of embarrassed that he allowed her to turn into someone who treats people that way.

I know everyone suggests disengagement but have you tried sitting down with her and having a heart to heart?

Ask her what changed.

My teens went through a period where I felt like they hated me. I had no idea what was going on, one moment they were my lovely little boys who adored me and the next I was the wicked witch of the west.

I think it's normal for teens to go through that. Teens are also the most self centred beings on the planet. They think the world revolves around them and owes them a living.
This isn't just a step thing, it's a teen thing.

Once my boys matured, we developed a great relationship. It takes time and maturity.

Your boyfriend is not very kind to you it seems. Otherwise this ALL of this would have stopped shortly after it began.

If my own daughter told me this I would be troubled. It is one thing to be kind, gracious and giving if that is your nature,,, it is other thing to be used AND a door mat.

ASk yourself, Am I as generious with my own bio family---cousins, nieces, nephews? OR am I trying to keep my boyfriend around???
JMO

As Evil3 says, your friends are wrong about your SD's sporadic contact being her way of saying sorry. Honestly? She's just looking for someone to use. It's pretty common behavior for Children Of Divorce, or any kids who've grown up around weak parents.

In steplife, there always seem to be clueless people around who want you to drink the koolaid and go with the dysfunctional flow. Don't listen to what anyone says, including your SO. Listen to your gut and rely on your own observations. You know this young adult mistreats you, so deal with it the way you'd deal with any other rude user. When she hits you up for something, try being direct yet neutral : "I'm surprised you've asked me for this favor SD, considering how you've made no secret of your dislike for me. What gives?"

I'm curious to know what her relationship with her dad is like. Is she spoiled? Is her BM an alienator? It seems as if in many cases of divorce, the quality of parenting becomes diluted as the parents vie for popularity. Kids aren't dumb and they're natural manipulators (especially females). If the skid is angry with her dad, she may have chosen you as an easier target for resentment, or BM may hate you. At any rate, most of us cannot rely on our weak SOs to handle these issues, and you are under no obligation to tolerate mistreatment. It does no good to live in hope that things will improve as skids mature, so you might be best served by quietly detaching from your SD. Don't be her whipping post or ATM.

I'm not seeing "sorry" in what your SD is doing in her treatment of you. I'm seeing the young lady say very clearly and loudly 'I am a user. I do not and will not appreciate anything you (SM) do for me, but hey, if you want to keep up paying my way and giving me handouts, *shrugs* works for me'.

I'm not going to tell you to stop doing these things. Whether you continue or not is on you. I assume you have your own reasons for allowing this grown young lady to financially and emotionally use you. If you want to keep doing it, keep doing it. If she has been rejecting you for over two years now I suspect you're doing it for a reason other than actually SD.

Are you feeling in doing all this help and assistance that you are instead really helping your DF? Are you afraid if you cease your relationship with your DF would suffer? Or perhaps you are just too kind to say 'no' and fear what your friends /family would think if you stopped enabling this young lady to walk all over you.

I will assume, since you took the time to seek out a stepparenting venting site, that you perhaps you are beginning to resent your situation. If you read around on the adult stepparent board, you will find lots of SMs who have either disengaged from their SD or are trying to. SO you can take comfort here knowing you are not the only one with a rejecting SD nor one who willing uses and abuses the relationship with their father/SM to get all they can manage to get out of the father/SM. And not at just age 18. Some of these SDs are still playing the game well into their 30s, 40s, and 50s.

I will say, if you're somehow waiting for this young lady to wake up one day and realize how good and loving you're been to her and how lucky she is to have you, yeah, that's really not ever going to happen.

I can only speak from experience. If I was doing things for the skids or spending money on the skids or giving the skids gifts or taking the skids out for dinner all is right with the world. If one thing goes wrong in their world, I am the wicked step mother who they hate. I took it for many, many years expecting that as they grew older and hopefully matured things would change. It felt like it was one step forward, thee steps back year after year. This year things to a turn for the worse because of SS so they are all now on the I hate SM band wagon.
I have never done anything to make these skids hate me they way that they do. My DH reminds them of all of the things that I have done for them over the years and guess what...they have never, ever thanked me! So with the help of the folks on this site I am so happy to know that I am not alone and I am learning to disengage.
One night I asked DH to tell me one nice thing that each of children had done for me over all of these years. He had no response because they have never, ever done or said one nice thing to me.

Welcome to Step Talk! Sorry to hear about your SD, but everyone who has already posted is right, she is using you - your fiance ought to have put a stop to it - and you should disengage. Plenty of advice about that from folks here, should you need it - good luck!
Remember, if you lay down, people will walk on you.

You can't stop her being a brat - its way too late for that. But you can stop her inflicting her brattiness upon you - sounds like you have already begun this process.

Disengage, stop doing anything for her, close you wallet and even block her from contacting you. She made it clear she does not like you, then why does she still like your money.

She's 18 and legally an adult, thus no need for you to do anything for her, disengage and close your wallet Hon.

She sounds exactly like my OSD

In fact, my OSD was great right up until about the age of 18, and then that's when it all started to go downhill with her

It escalated to open hostility and public displays of hatred towards me

This went on for a few years and then she "changed" and like yours now, started to supposedly be acting civilly towards me

Do not get sucked in. She has shown you who she is, and what she thinks of you

I doubt she is truly sorry in any way. She's just putting on an act right now for her own means

And when she feels like it, she'll turn on the hatred again

Don't be a doormat. Be forgiving and understanding, but do not accept her unacceptable behaviour towards you

The more you show her that you're okay with her disrespect and will continue to let it all go, the more she knows she can get away with it. Demand respect as a human being, at a minimum

The only thing that has ever worked when it comes to my OSD is to disengage from her.

She hates that. She hates it because she loses her power over me. She can't manipulate me. So she tries playing nice and in the past when I've fallen for it, she goes right back to sticking it to me.

I haven't reengaged for a long time now, and she has pretty much given up the nice act. Now she's in all out nasty mode

And it still won't get her anywhere with me. It will just result in me disengaging more and more...and when I disengage to that extent, eventually her Dad (DH) does the same thing. She really hates that

Always be the class and don't succumb to your SD's tactics, but don't be a doormat. Walk away from her disrespect and manipulation

Advice???? Cut toxic people out of your life. For sure you dont help toxic assholes. So quit helping SD-18. Throw her comments back in her face when she comes crawling back to beg for support. "I no longer like the person you are and no one can make me support or care about you"..... lather, rinse, repeat.

Quit volunteering to be her beck and call support bitch/victim. People are treated commensurate with their behavior. She has earned nothing but your contempt and to be cut off because of her behavior.

Stick to your guns... and have fun rubbing her nose in her own stench. }:)

Welcome by the way. I hope that you find this to be a good place to vent, contribute, and to pick up some useful perspective from others who are living the blended family dream and adventure.

I wouldn’t support her anymore either. Her actual parents can deal with that.  Even though they should be making her learn responsibility in the process. That’s a struggle in our house. My fiance’s son and I got along great until we bought a house together and I expected him to clean up after himself. He’s almost 16. The other issue is that I don’t tolerate his lies and disrespect but his dad babies it. 

I have an sd17, who over the years has become more and more hateful to me and my bios. her sister is the complete opposite. anyway she has turned into a master manipulator and her mother is unmedicated bipolar who preaches hate and hostility and my sd17 is following that exact same path. this year , to save my own sanity, i disengaged. occasionally my dh gets mad , for instance if there's an appointment she needs to go to and he has to take off work to do it, but again, it has saved my own sanity. I can't change anyone who is on a destructive path, especially when they have been shown the way to a positive future and decide to take the negative one instead. that's on them. 

We have a saying here “Ignore the whore”.   Doesn’t imply anyone is a whore. Just rhymes better than “Ignore the bitch”. 

She is using you of course, and she is probably laughing her ass off and ridiculing you to anyone who will listen about how stupid you are and how she can manipulate you. 

Just remove her from your life. You can block her on social media and your phone. Be polite and civil if you cannot avoid being around her. No need to announce anything. No more gifts. No more favors. 

Just let her be someone you once knew. 

I feel for you! seems you were so nice and generous-and got bratty , selfish & harsh treatment from an ungrateful teen! I have been there many times with my teen SD. Thank sweet jesus she does not live with us on a full time basis, but a few weeks at a time is enough! I eventually stopped going out of my way to get her special gifts or treat her nicely, bc she was still the same bitch after-and rarely appreciated anything! Her parents can do the gifts, money etc. and she gets plenty-so I am done! And, believe me it has been hard resisting the urge to get her something nice for her special bdays and holidays-but this past Christmas pretty much sealed her fate in the no-gifting zone! Plus she rarely acknowledges family birthdays or holidays-so it's  over. I'm done and so happy with my decision.