The OP said the FA had an attitude from the time they boarded and was unpleasant from the get-go. There's no excuse for that or the way the FA acted over the drink situation. Sounds like she was being <redacted> the way she talked if the OP is to be believed. She can determine if this was a case of child trafficking without being snotty.

I do agree that a word to the crew of the situation might have saved some of the drama. I have a grand niece who is schizophrenic and also on the Autism Spectrum and that's not an easy situation either but her mother does tell the crew about her condition to avoid any unpleasantness.