Your kids don't treat you this way because they never had anyone around them who sanctioned treating you this way. You have a husband problem not a step kid problem. 

" My husband most the time never takes my back on anything and calls me out in front of her it makes me look stupid."

^^^this is the absolute oposite of what a good husband (and parent) would do. My husband ALWAYS has my back in front of his daughter, he had backed me up even when he has disagreed with me. Later we may talk about things, but in front of his kid, we are a unit that operate as one. I would never let a child talk to me as though I am nobody and I know my husband would never alow it either if his daughter dared to do it. 

If your husband cannot see that he is raising his daughter to be disrespectful and that he is endangering his mariage by his actions then it probably is time for a superb therapist or a divorce lawyer. 

I have a very similar situation with my SD 14. But the BM is the one who encourages the disrespect.   I love my SO so ending our relationship is not an option.  I've chosen to disengage.  It's not been an easy process but I have read several books and feel at peace with my decision. I am happier than I have been in a long time and SO and I are getting along so much better. I will not let a disrespectful, ungrateful teenager have that kind power over my life.

The question is not why can't you love your SD - because the answer to that is obvious - she behaves in a foul and abusive way towards you.  The real question is why do you love a man who allows and promotes this?  I'm sorry to say but if you make yourself into a doormat, people are going to walk all over you.  Try to develop a wee bit of self love and remove yourself from this toxic situation with this misogynist who encourages abuse of you. 

I know that one day that she's going to be the reason why we split up

No, HE will be the reason why you split up.

He calls you out in front of her and makes you look stupid? He lets his daughter treat your horribly and talk to you like a nobody? Is that what you think love is? Is that the way that YOU would treat someone that you love?

Do the two of you make decisions together when it comes to issues you are having with her? I'm in a very hard situation and feel pretty much the same way you do. I had to start talking to my fiancé, just the two of us, about issues with the kids. After that, one of us or both of us will confront them. This is working better than other tactics in the past. Only problem is he usually feels like I'm attacking his kids when I first bring something up. FYI, these are 3 "adult" children living in our tiny home. I told him we need to come up with a plan to get them out of the house. He's finally coming around and seeing some of the problems.

I understand not wanting to leave him. I can't imagine my life without my fiancé, but he has to figure out how to balance his role as a father along with his role as a husband. You have to demand that from him. He also needs to learn that decisions should be made between the two of you. That discussion takes place behind closed doors and then both of you make sure to keep her in line.