Umm…so you are friends with this girl’s mom and dad? Or are her parents friends with your parents?
She’s not related to you by blood or marriage…and “friendships” end all the time. I’m assuming that your parents are friends with the girl’s parents. If I’m right, then I don’t see why its so difficult for you to cut off contact with her. I’m assuming that you’re also in your early 20’s…so as an adult, explain to your parents why you refuse to deal with this girl and her drama.
And if she keeps talking trash about you…then let her. Your friends and people in your community who know you will know that she’s full of s**t.