ESH

As a keeper of small humans (who doesn't really like other adult humans or their offspring) I try to be conscious of my kiddos behaviour out and about. That said, sometimes you have a horrendous day and everything goes A over T. I know that juggling multiple tiny dictators (and an I'll one to boot) in a confined space for an indefinite time is enough to make me lose all sense of time. And empathy. So maybe, this Mum had a hellish day which was tipped off by being a human good dispenser in a room of sick people. That said, she clearly gave no fcks about what *her kids were up to which is kinda sad.

It sounds like potentially this girl had a behaviour disorder or was a little slower on the uptake as generally a stern word is enough. This kid sound stressful.

But, also, you kinda suck OP. Not for standing your ground, and not for defending your new tiny baby from a ham-fisted shouty human. But for yelling at the kid. I'd talk to the mum next time. Sounds like this kid wanted attention and obviously wasn't get it else.

And failing this, yell at the mum. She's an adult, she can take it.