Justbecauseitsso I am sorry this is happening, it is hard.
RedSkyAtNight has it.
Please can I add that if this is an issue for you (clearly it is), please get some counselling. Get motivated to get involved in the school if you can (fundraising, parent/teacher whatever) and then you can be in the centre of things a bit. But do get some counselling to deal with some of these issues for you, as I do think you are in danger of passing this form of (perhaps) 'anxiety' on to your dd.
carolinescustard that is so appalling. What did the teacher do, I would have complained to the school for allowing that. I hope your son is in a nicer school now.
LittleIda that is awful and I think the teacher should have stepped in and said that things like that happen outside the school, not in it.
OP it is only being excluded if all the children or all the girls in class are invited.
"I know in my sensible rational mind that it's no biggie and this is just the beginning of the road to many more types of worse rejection."
This is a really negative way of viewing things in life, please find a way to re-think this. We cannot all do everything and learning to deal with life's ups and downs is a vital life lesson.
"It's the hurt of all my own past rejections at school rearing their ugly heads and trying to project themselves onto my dd."
Are these hurts that you experienced or your dd experienced?
I was very shy as a child and had few friends. I had OCD as a teenager and now as an adult have an eating disorder. I am getting counselling for this and it covers the things that happened as a child. (Just not being that included etc). There is help and one can process these things better with help.
"And yes I admit I'm wondering why this particular mum has decided to exclude my dd and yes I'm taking it personally." Would you consider asking her, could you cope with that? Could you ask if you or dd have done something? I am notnecessarily recommending this course of action but if your dd is friends with the child you could just ask if the mum thinks there is a reason not to include her?
The action of asking could lead to ill feeling from the other mum, she could tell others you had tried to get an invite by making her feel guilty, she could invite your child but you still feel it was under sufferance etc. I am not recommending asking but if in future you sense the other mum has something against you, you could ask.