How to deal with being involved with someone who has a mother who interferes?

I've been with my girlfriend for quite a while now and we've been through a lot together. I've tried to just deal with her mother. But her mother is totally against gays and tells Ericka that she's going to hell for this. She's the type that's really nice to your face but then talks hatefully about you behind your back. She's always trying to get away from this lifestyle and everything. Ericka is 21 and she came out to her mom when she was 17 and her mom is still treating her rude about it. Also her mom treats her as if she's 12 years old. She still punishes her and guilt trips her into hanging out with her and all that motherly stuff. But the fact that she doesn't let Ericka live her own life and the fact that she's totally rude about our lifestyle just really interferes with our relationship. How do you deal with your girlfriends/boyfriends mom that you cannot stand?How to deal with being involved with someone who has a mother who interferes?
the hateful mother will not change their mind. you just need to ignore it, this relationship is between u and ur gf, nobody else.