I think if they were meeting by chance, like in school, it would perfectly acceptable to leave them to it, but if your child doesn't want to go to someone's house, I think I would listen to that. DD won't really have a socially acceptable way out. I just wouldn't go. I wouldn't tell your neighbour this though because parenting is a marathon, not a sprint, and you never know when they might be in a situation together so you don't want to burn any bridges.
If you want to still be friends with the mum, see if she fancies going out for a drink without the kids. Might it be less intense if you all went somewhere neutral? Three is a really awkward number sometimes.
I wouldn't talk to the neighbour because I don't think there will be much she can do about it, rather than both of you policing how the kids are playing, which is no fun for anyone.
If her DD does turn out to be ND, that might explain things but it won't make your DD want to be her friend and I think it is really important you encourage your DD to listen to her intuition about friends. When she is a teenager, you'll be glad she has. Whilst we should be polite to everyone, you actually shouldn't be friends with people who upset you, as Mumsnet threads about adult friendships suggest.
Sadly, mum friends work best when the kids just get on. I think it's too much of a stretch if they fundamentally don't. Sorry, OP. This is hard.