Quote
has cut multiple very close friends and family out of her life, and always seems to be your "bestie"...until she's not.

Saw this in your intro to this thread. Have you ever heard of borderline personality disorder? People with this issue can “swing” - first you’re the best thing since sliced bread, the only person who really understands them - then you’re a horrible person, the worst ever.

People with borderline personality disorder often cannot maintain stability in their lives, or do so with difficulty. They don’t maintain friendships well over the long term. They have difficulties with coworkers at work. If you were the subject of their admiration at first, it’s disorienting when they turn in you.

I suggest you read up on it and see if it rings any bells. If she IS BPD, understanding it will be key to helping your kids in the future.