I think your situation involves a lot of different questions with different answers. I did vote YABU purely because the ultimate question of was it rude to me is no but I don’t think that quite captures what happened.
Firstly, is it rude for the mum not to message you herself - I would say slightly but not really. I can imagine several mums I know who wouldn’t think/have time to do this - they may just think it doesn’t really matter and just assume as it’s a play date it’s all fine.
It wasn’t a social occasion just for you two, although of course that would have been an added bonus for you both to chat as well and was clearly part of your invite. But it was probably just secondary in her mind to the play date and she wanted that to go ahead as planned even if she couldn’t make it.
Secondly, is it unreasonable to feel put out at a stranger arriving (putting aside your trauma for a second) - no, I would find this unbearable from a social point of view to expect to host someone I didn’t know for such a long time. It would make me incredibly awkward. What the hell do you talk to someone you don’t know about for that length of time?! I’d just have to put the TV on and leave them to it or make up some emergency to get him out. If he was going to stay then cut it down to 45 minutes not 2 hours!!
But most importantly is it reasonable for you to feel the way you do about this - absolutely, as you have gone through the most hideous trauma and are doing your best. I am so impressed by how well you coped at I can’t even begin to imagine how scary it must have been. You don’t owe anyone an explanation - mumsnet can be cruel as people are emboldened by anonymity but you really did so well and it shows what a dedicated mother you are to power through like you did.
I think your instinct to move play dates out of the home is perfectly fair until or unless it’s someone you know and trust and who knows your feelings and who wouldn’t (no matter how innocently) put you in this situation.