That poor woman! It makes me spitting with rage. I hope she gets proper support and the head takes this seriously.
I was venting my spleen to my teacher-DH and he added that if she's a teacher she might have a decent union rep, who would be worth contacting with this. Of course some are better than others, but in my experience they've been (1) women and (2) bloody brilliant on this kind of thing. He thinks that if the head's got any grip on reality the TA will be shifted to another class, at the least, and hopefully some kind of disciplinary proceedings too.
On a side-note, Bidisha, I spent ages after reading your post thinking about the power of kindness, of empathy, and of being believed and supported. What the 'feminists are angry and nasty' crowd just don't get is the power of, for want of a better word, sisterhood. I'm thinking this out as I write and not feeling very articulate this morning, but it's part of the power of #WeBelieveYou - that sense that no, you're not alone, not making this up, not going mad - the world really is against you if you're female, but we've got your back, and we believe you.... it's an extraordinarily powerful and important feeling.