We had an incident with a stepmother, who came to our house when dd was 11 (end of year 7) and ranted at me in a high-pitched squeal for 7/8 minutes without me being able to get a word in edgeways. Then turned on her heel and left. She was upset that my dd had introduced her dsd a porn grooming site, which has since been removed from the internet, that her dsd had subsequently shown to a 7 yo niece. Except my dd hadn’t introduced it to her dd. My dd there at the time but she thought it was disgusting. Otoh, the dsd was intrigued. (No blame is apportioned to this as at 11 I get she was just curious without understanding the implications.) It was a mutual friend, who had shared it… and another friend of my dd and that friend, who had shown it to her etc etc - as is the case with such things. I never outed that friend as I wasn’t going to send batshit woman to their door.
I had another visit from the batshit woman last year. Similar tone of voice etc. I said something she didn’t like, which escalated the situation. She left slamming the door so hard that it flew open again. Then the texts started. I replied once with a firm boundary and she flew off the handle, telling me I was 50% to blame for my dd having anorexia.
Unsurprisingly her dsd (girls both now 16) is not terribly emotionally stable. My dd put up with her mood swings for a long time. They’d been friends for 12 years. It blew up this year. Nothing dd did. Actually the dsd hounded one of dd’s friends, calling the friend nasty names. That friend ended up telling the dsd that my dd had said horrible things to her about this girl (all untrue as dd said she hadn’t, the friend just made it up). At the time my dd was incredibly ill with anorexia and it wouldn’t have entered her head to say such things, she was barely functioning. This completely blew up the friendship and the dsd sent my dd the most vile message I’ve ever read in my life. Such venom from a 16 year old is unreal. The text started by telling my dd (who had lost almost 30% of her body weight) to starve herself again as she is putting on weight. Suffice to say, they are no longer friends.
You have put up a good boundary for your dd. I learned very early on that any incidents, which happen at school should be addressed through the school to prevent upsets between adults. The children have often made up before the parents even fall out. And I learned from the interactions with this woman (who I was loosely friends with and forgave the first incident), that when people tell you who they are the first time, you should believe them.