Speaking as a mum with two children with learning disabilities , I have a couple times been in a situation similar to this when I can't cope and make questionable choices.
Can you imagine beings stressed and at the end of your tether that you behave like this woman behaved IN PUBLIC, in full view of the playground. It's traumatising.
I remember one terrible home time when similar happened to me. My children had been awful running away, hitting me, hitting each other, everyone was screaming, it was hell. I'd been being patient for about hour already and had only managed to get them half of the 10 minute walk home and we'd needed to wait in the playground until everyone else had left in order that everyone calmed down. Started to walk home again and we had to go into the supermarket to get something important. It all kicked off again with the children running round the shop uncontrollably, screaming and fighting. Eventually I cracked , and when one child went to attack another for the umteempth time I pushed him over and he banged his head on the floor. He started screaming, so I hauled him up and pulled him screaming out of the shop, whilst holding the other screaming child's hand too. A woman came over and started to admonish me. and through angry, embarrassed, stressed tears I reacted very similarly to the woman you encountered .I think I said : "Please, this is none of your business and you know nothing about the context of this situation. Please don't judge me". Luckily at that point one of the teachers from my children's school came and helped me at that point because I completely lost it, crying in public is horrible.
The woman came and apologised afterwards.
Don't judge until you've been there.
Don't judge and make it about you.
It's difficult to imagine just how stressful it is to have a child with behavioural issues.
Report it to the school and trust the school deal with it.