Their response (linked by others) is probably the best they could do. But also it looks like they are taking her allegations seriously themselves.
This is my point. Even if she is wrong, they would have to pretend she is right. There is no way of them saying "She overreacted and tried to play 'harrassed woman' card when in reality she was just bad'.
And regarding 'influential developer'... "influential developer known for helping make GitHub a more attractive place for women programmers to work". Sounds like she was known for being women activist and influencing the view of the company in female circles, rather than influencing the code base/architecture/whatever. She _might_ be a very good developer - I just don't see it claimed anywhere yet.
Issue is that it is not any longer possible to say "this particular woman is horrible and crap programmer" without being understood as "all women are horrible programmers and I'm chauvinist pig". And while I agree that industry is quite sexist and in many cases attacks are underserved, I refuse to give special handling to a worker doing bad job just because he/she comes from some opressed minority.
To be honest, I would find it a lot more sexist to give the hell to the guy producing bad code routinely, while being all time calm, smiling and forgiving to woman doing same thing. I'm probably 'chauvinist' enough to put a line at physical violence (like effectively defending myself against physical assault of man versus assult of women), but I'm not going to hold back on opinions just because of gender (or color of skin, disability or sexual orientation).
Again - not saying she is bad. I'm just stressing that in current PR climate, we will probably never learn, because it will be always better for company to sacrifice a good male programmer than try to fight to expose bad female programmer publicly.