Mean Girls

Deborah has a problem kid at school. I want to remind you that Deborah is 4 and in pre-school.
This other child, who shall remain nameless, will now and forever be called 'J' in my blog...
J has had a very difficult child-hood: living with a foster family, now returned to her parents... Also, her foster family had three teenage girls, so she's been around the whole "boys, makeup & hair-do's, and clique" type attitude.
J likes to control most of the other kids around her, and does this by 'letting' them or not 'letting' them play with her. At first she and Deborah were friends, but they've gone through this whole 'I'm your friend now, but tomorrow I won't be' thing.
She has called Deborah 'fat' and 'stupid'. Words completely unacceptable in school and in our home.
We've asked Deborah to avoid playing with this other girl, but this has led to her kind of being a pariah in her class...
We've talked to her teacher, who is very concerned about the situation. She knew something was going one, but didn't know how much it's affecting Deborah. Miss Emily is working on teaching the kids about feelings, hurting each other's feelings, and kind vs. unkind words.
Right now, I'm having a battle with Deborah every morning about going to school. I HATE making her go to school. I know how bad this all feels, 'cuz I had two girls who did similar things to me- one in kindergarten and one in 2nd grade. When you're a kid in the middle of this kind of mess, it's HUGE.
Anyway, this is what's going on here...