Not much to add, except I empathize! We're going through a similar, though milder, situation with Hanni, age 4. There's a girl at preschool that she adores, but who treats her meanly *some* of the time, but is wonderfully fun the rest of the time. It's like an addiction with Hanni. I can't get her to see that she might be happier if she walked away and played with someone else.
I've been somewhat hampered in my efforts to intervene by not wanting to trash-talk this other girl. We've known her since she was a baby, and I think she's picked up mean-girl behaviors because she's been dumped on by her older sister. She's only 4, and I want to believe she is basically lovable, just having a hard time with her own stuff.
But recently both of Hanni's teachers (independently of each other) all but came out and said: T is a mean kid, Hanni should stay away from her. It kind of shocked me, but I also found it kind of liberating. Maybe I can be more blunt with Hanni about how T is treating her. T deserves sympathy and help with learning better behavior, but my main concern has to be Hanni.
