Most Helpful Girl
You definitely weren't wrong. Emotional abusers always get others to do their dirty work (I. e. her mom)
Most Helpful Guy
You shouldn't just cut off all communication, but you should tell her that it makes you incredibly uncomfortable and that if she respects your feelings she won't have contact with that person, but that if she wants to continue to live like that she can do it without you because you're not going to put yourself through that.