It seems like the major source of antipathy towards her was the firing of Victoria Taylor, which happened on her watch, but was actually done by a man who is still at the company, and nobody seems to want him fired. It's entirely possible I have some or all of my facts wrong, but this is what I understand to be the case.
The point of leadership is to deal with these sorts of issues, and take those hits when they don't pan out. It's like having your cake and eating it. On the one hand, we use the excuse: "just doing his/her job" or "just following orders", and then on the other hand: "Happened on his/her watch, by a subordinate", as if it makes it okay. The blame needs to be shared (if appropriate), and not shoved around depending on which side we are currently arguing for/against.
That's when most people started hearing about it outside of Reddit, but I guarantee there is been strong hate before any of that happened. And it really does seem gender-based, or at least those are all the primary attacks.