Sounds like the kind of "mother" one would be glad moved across the country. Next time she says something hurtful, I would reply in kind and then not bother trying to continue the conversation, just say you have to go now, goodbye, and then hang up. I would not give her the last word.

"I moved across the country just to get away from you girls" deserves a, "Yes, and we're very glad you did, thank you."