"Blood coming out of her eyes" seems to imply she's "bloodthirsty", out to "get him" or something like that. I don't see any sexism there.
People usually omit that first part, and falsly quite him as saying "blood coming out of her whatever", which sure does sound very sexist. But if you quote the whole thing, "blood coming out of her eyes, or whatever" sounds like he's basically backtracking on his (too) offensive comment.
I've been thinking about this... I still don't think he was referring to her vagina, but I admit that I could be wrong.
However, even if he was, or let's make it clearer, even if he directly said "she was so mean because she had PMS/her period", that would still not make it sexism. Sexism is discrimination on the basis of sex. Trump wasn't discriminating against her, he was insulting her because he disliked her (which he's free to do, of course).
For insults to be effective, they have to be tailored. You won't call "gay" an obviously gay guy, because that's not an insult, that's the truth! The insult "gay" would only be effective towards someone who's masculine and exaggerates a bit, making you believe that he's actually insecure of his masculinity and would be hurt and offended when being called "gay". That doesn't mean you're homophobic, it just means you're good at insulting people.
Trump was simply tailoring his insults to her, and if he meant something in connection with her sex, that's no worse than insulting any other part of her. He's obviously not discriminating - he's been insulting pretty much everyone, and his insults are always highly tailored ("low energy" Jeb, "crooked" Hillary, ...).
People usually omit that first part, and falsly quite him as saying "blood coming out of her whatever", which sure does sound very sexist. But if you quote the whole thing, "blood coming out of her eyes, or whatever" sounds like he's basically backtracking on his (too) offensive comment.