When my SS was 14 and saying he wanted to live with us, people on here warned me that he wasn't an innocent victim, he was manipulating too.  Boy were they right.  It was easy to put all the blame on BM, but he definitely was part of the problem.

When she comes over, just be polite and pleasant and do your own thing. If she apologizes (she might), say, "thanks" and still be polite and pleasant and do your own thing. 

You tried. That's all you could do.

Stick to disengagement. Be polite and kind, but direct SD14 to her father if she needs anything.  I doubt she'll get what she needs there, but that's not your problem.  Don't buy her things; don't go out of your way for her.  She lost that benefit - well, more like she threw it away.  Stay out of her schoolwork - let her sink or swim. You're a kind, giving person; find a worthwhile project or cause to invest your time and heart in.  SD14 isn't it. 

Remember,  this isn't a one time thing,  it's a pattern.  That pattern has been in your blogs for a long time. If she's uncomfortable in your home, it's her fault. 14 is old enough to comprehend cause and effect.  You tied yourself in knots for this kid and she threw you under the bus.  Everyone will blame you, but just ignore them.  Your only crime is to not be dysfunctional like the rest of them.  

I remember being your SD's age and my mother talked to me about "punishments and personal responsibility".

What she said was that she was basically done "punishing me" that anything I did or did not do would have more impact on me than any punishment that there would be consequences of my actions and even if she wanted to, there may be consequences that she can't fix or make better.  

She told me that while my parents expected me to do well in school... and would be disappointed if i didn't do my best.. in the end, it wasn't going to impact THEM.. They had their college and master's degrees.. They did the hard work that enabled them to get into Harvard.. etc...  So, I don't study.. slack off... get held back.. that's on ME.. not them.. and if I can't go to the college of my choice.. it's my fault and they can't fix that.

If I break the law.. I am the one that will get that mark on my record.. have to pay the price.

If I do drugs and OD.. I'm the one that may be arrested.. or die..  I'm the one that will risk life limiting choices in my young life.

If I get pregnant.. well... again... that's me.. not them.. and I will suffer those consequences.

Basically, I had gotten to an age where the stakes for me were higher than they were for my parents.  Now, they said that part of the parent/child deal was that they gave me privileges.. and if I abused the privileges.. they would be taken away... (we didn't have phone.. really more talking about allowance for me).  That it was up to ME to think about my actions and what the result would be on my life.

If/When Munchkin decides that her other life is too toxic and wants a break... you can give her that message

M.. in the past, I have tried to manage things that were things you really should have been doing for yourself, I'm sorry if you feel I put undo stress on you or unrealistic expectations.  Going forward, I hope that you choose to excel in school and keep your nose clean because I know you are a smart and capable person with great potential.  But, I'm no longer going to push or ride you to get the best from you.  you need to want it for yourself.  Of course I will be disappointed if you don't do what's best, but I think you need to understand that at this point in your life, your decisions will impact your future.. for the good or bad and it's up to YOU to choose wisely.  I have my life, my home, my career, my family.. it's up to you what you make of yours.

I'm not going to punish you for those things either.  Don't get me wrong, if you abuse a privilege like your cell phone, your dad may decide you can go without it for a while.. but making good choices? doing your schoolwork? You are the only one that can truly make those decisions and I hope you choose wisely.. but in the end.. it's your life.

I hope you are truly done this time, Clove. You cannot fix her.

If you don't keep your boundaries in place, these tantrums of hers will only get worse and it will only be a matter of time before she and TT are accusing you of something more serious.

I have been where you are, trying to provide a better path so SD can have a better life. But, they cannot get out of their own way and their loyalty to their dysfunctional, mentally disordered BMs, keep them from accepting guidance from us or their fathers.

My SD was 15 when she declared her little war. She even tried to get DH to hit her. I'm sure BM orchestrated the whole thing, as it was very out of character for my SD. Yes, I was hurt (seemed she believed all of BM's lies) but I got over it and became indifferent and never trusted her, again. I am indifferent to this day (SD is almost 30). I don't want anything bad to happen in her life but I don't lose any sleep thinking about her, either.

When my SD was young, I would have bet my life that she would be more like my DH but BM's influence was too hard to ignore, I guess.

Is playing one side against the other.  Telling BM what she wants to hear and you what you want to hear. Telling both of you how great you are to her,  until you want her to do something she doesn't want to do. Ie school work.  Then you are evil SM. As BM and her sister are evil BM and evil sister.

I would not pay her phone bill. I would cut her off you disrespect me you get nothing. Let her bio parents work it out. 
you must disengage from her and her sick ways. Do nothing except say hello and better good by.

DH is now in charge of cooking, cleaning as in everything 

Cut her phone off..TT and your DH can figure out how to get her a phone.  When GWR pulled his "I want to live at mommies house" we shut off his phone, repossed it, took his car and gave that away, stopped his car insurance.  No respect..no rewards...go get mommy to pay for your crap.

CLove, what is your plan when Munchkin comes over and says, "TT told me to say all of that."  I'd expect that from her. 

A couple of weeks ago this kid was upset because FF assaulted her, and she didn't want it swept under the rug as proposed by your DH.

Now she is complaining you are "harassing her in her bedroom".  Umm, isn't that a bedroom you help pay for?  And weren't you asking if she got her schoolwork done?

You've done so much for this kid.  You've been a safe haven for her.  Let go of the rope, and let her parents deal with the mess they created.

SD is 14 and well aware what she is doing.   And to whether she comes back and blames TT or her sister it really doesn't matter at the end of the day  SHE has done this behaviour and therefore any consequenses that happen to HER is HER own fault.

Show her what her behaviour achieves by removing yourself from her life, if she trys to crawl back and blame everyone else tell "No you are 14 YOU knew what you were doing and untill you take responsilbity for YOUR own action and stop blaming others and maybe we can talk about again."   But don't reengage with her keep every thing between her parents you can't care more then they do.

You know this behaviour cycle will continue unless you stop it.   Remove yourself from all points of contact for her, disengage from her when she at your home, let her and her parents figure out her schooling.    

I'm really sorry it has come to this, but I understand what you are going through, I went through it myself. When I disengaged from Spawn I think she figured things would be back to normal in a day or two. I have a feeling TTS will probably think the same thing, that she will do this, you will get over it and forgive her and in a few days things will be normal again. I know Spawn thought this with me, she was 16 when I disengaged and I have not spoken to her since that time.