This reminds me of a swim-birthday party my DD was invited to last year. I've known the dad forever and his parents and I've become good friends with the mom. Their youngest daughter went to preschool with our DD and they really hit it off. After that first year of preschool they switched their DD to a different school. The girls now rarely see each other but they invited us to the birthday party anyway. Well I didn't know any of the other parents at the party (who all knew each other) and DD didn't know any of the other girls. Fortunately my DD is funny and can find a way to fit in anywhere and by the end of the party she OWNED the birthday girl. But I was nervous for most of the party that she would feel left out.
I mention this because I thought it might help you feel better. Hugs to you and your daughter.
" I object to violence because when it appears to do good, the good is only temporary; the evil it does is permanent." Mahatma Gandhi
"This is the ultimate weakness of violence: It multiplies evil and violence in the universe. It doesn't solve any problems." Martin Luther King, Jr.