I doubt she was there to see you. She wanted to see her grandchildren. She’s probably just a bit disappointed their mother is so unpleasant.
Way to speak to a traumatized new mother. I hope some of the posters making these comments are proud of their bullying - and yes, bullying is exactly what is is. That's not to include those who for whatever reason agree OP is being unreasonable, and have stated so in robust but polite terms, nor the ones who are recommending she considers therapy. But it certainly includes posters like this, or others who are making deeply derogatory comments attacking her in the most personal terms, or telling her her mother 'couldn't give a stuff about you'. Nice. Real nice.
These people need to take a close look at themselves and ask who the mean kids at their school really were, and also whether they'd want their own children to be the targets of such meanness; whether they feel they're 'reasonable' in their stances or anger, or not.
This OP has suffered a very recent and extreme trauma, and is posting on a site which might be her only way of venting her anger. (Nb. it's sod all to do with anyone else how much time she spends online. I sat on my arse for hours at a time breastfeeding my newborn. If Mumsnet want to police how many threads and on what topics a member posts on here, that's their job.)
Before anyone points it out, I know the reputation of Mumsnet and AIBU, and that anyone posting here better be prepared for what's coming to them. It's reasonable to expect you are going to hear some things you don't want to hear. What you shouldn't have to expect - ever - is en-masse bullying from supposed grown adults who should know better.
OP, I fully understand your anger and your need to vent.
As for some of the others? You disgust me.