The actual sexism in it seems overblown at best. They had a party, girls were hulu-hooping, guys stared. She seems to somehow have been shocked and perturbed by this, which makes me wonder about her. Is she shocked and perturbed by the affects of gravity or the inverse square law as well? Yet this completely unremarkable scene is cited as the 'last straw' before she left.
For the most part the real problem appears to have been a founders wife. FTFA: "In her email to TechCrunch, Horvath says she felt "confused and insulted to think that a woman who was not employed by my company was pulling the strings." She also said she felt bullied by someone with perceived power and influence over her personal relationship and her career at GitHub."
Now I dont know about where Julia is from, but here on Earth a founders spouse having what might be technically inappropriate involvement in the company business is not exactly unheard of. It's also typical for that spouse to have what we gamers would describe as a great intrigue score - a manipulative deceitful personality that will bluff or lie about her current position in order to improve her position 10 moves later in her game, and who will use you up and throw you away without a hint of remorse if she sees a gain in it. This sort of woman is always scheming, and employees that just want to keep punching their clock and spending their paycheck have to be vigilant to avoid getting involved in her schemes, usually to their detriment.
Now I dont blame our heroine for being uncomfortable in that spot, Everyone is. I am just saying it's odd that she would actually be surprised by something so common, and odder still that she would attribute it to sexism.
Github indicates the spouse in question has been dealt with, so frankly it sounds like they may have won on both ends of the deal. Seems an easy bet that at least some of the employees are breathing much more easily in the office today with both of these ladies gone from it.