How do you deal with your significant other's parents when you live in their house?

Ive been living with my Girlfriend and her mom for about a year now, and things that I thought would have improved, have not yet. I need some suggestions that would help me make my stay in the house a little more pleasant. Her mom is extremely picky. All she does is complain to my GF about the dumbest shit. The best part is that she won’t talk to me about issues. She just goes behind my back and talks shit on me. I know this because I’ve caught her and confronted her about it. After I confronted her, I told her that I didn’t appreciate it, and that there is a clear lack of respect. I even told her that if there is something that I am doing, or need to change, to please tell me to my face, instead of bad mouthing me to others, but she won’t listen. Please Help!