Here is the back story:
We live in America in a town which is prosperous. Most parents are making at least £100k+ a year and are quite showy sometimes depending on their wealth/cultural background.
DD is in a special needs class (ABA) and is the only girl with six boys. She is very high functioning with a diagnosis of ADD/ASD/anxiety and oppositional defiance. To give colour, she will turn 7 in July and her reading age is 10.4. She finished grade 2 mid May and is a third of her way through 3rd grade. She has zero social skills and I fight tooth and nail for the school to work on social skills with her because this is her most significant weakness.
On Sunday a boy from her class had a party for celebrate his birthday. Everyone from her class except her was invited and attended. This morning DD didn't want to get out of bed because she didn't want to go to school. She said her heart was broken because she wasn't invited to the birthday party. DD told me the verbal boys were talking about it yesterday in class. The birthday boy is not verbal.
What I've done is tell DD that birthday boy is not verbal so couldn't tell his parents to invite her. Her reply to me was that DS (my son has a diagnosis of ASD and is in a different ABA class) class was all invited too except DS.
I've seen the pictures on FB now that I've looked. As far as I'm concerned the mother is a first rate bitch who can rot in hell. I'll kill her with kindness because that's how I deal with people like that. She has previously made snide remarks about me demanding the school district provide therapy rather than us pay for it privately. I had complained about the school removing therapy from my son and had gone to the parents group for suggestions as I couldn't find qualified therapists available on weekends. Her suggestions was 'we all make sacrifices for our chilldren. You are choosing to put yourself first by working. Don't work and you won't have a problem scheduling therapy.' 
She is South American and from a well to do family, doesn't work outside the home and her other NT child attends the local private school.
DH wants to talk to the school and ask them to talk to parents about being inclusive. I've told him it's life and the only person who needs to be aware is the teacher so she can manage any meltdowns. DH would like to exclude the child from DDs birthday in July. Again I think the way you deal with people like this who are like a hospital gown is to invite them, be super nice and hope they realize the mistake they have made.
WWYD?