My girlfriend hates my mom what should I do?

Basically me and my girlfriend have been dating for a lil over a year on and off. My mom and I are very close, so she insist on making jokes about how close we are and crap. Her and her mom however are not close, and so I really don't think she understands. Her mom is very moody type person and pushes her away all the time. She recently told her she could not see me anymore because she didnt approve. So what I dont get is how she hates my mom so much when my mom hasnt said anything about her, but takes up for her mom who's banned her from me. Her dad who is a crackhead and in and out of her life recently tried to charge me with dating someone younger, he didnt go through with this but he threatned it. So basically since then she all the sudden hates my mom and crap.