BABY MOMMA DRAMA PLEASE HELP!

Okay, so I've been with my husband for 5 1/2 years now. He has a 5 1/12 year old daughter. (We started dating when she was 2 weeks old). And I've been in there lives ever since. Baby momma and I don't get along only because she believes I "play mommy". We have the majority custody so she's almost always with us, and I definitely love her like my own. I've never gone around saying she's my kid and blah blah blah but BM thinks I do. And she also thinks I taught my step daughter to call me mommy. I don't wanna take her place nor do I try to. She expects me to not discipline her, not to cook, not to play or provide for her. She's literally said "you should just be her friend and nothing more". I'm pretty sick of this and so is my husband. She'll make a point to make sure to tell my step daughter that me, my parents and my siblings are not her family. And it's really breaks my SDs heart because she's so confused 😔 any thoughts how to handle this? Aside from hitting her with my car?