Perhaps she signed-off her email/post/comment with a female name? You know, it is perfectly reasonable to assume gender when the name is obvious. E.g. the odds of a person called "Samantha" being male are miniscule compared to it being a female. Because in both cases, "it" is a person we are talking about.

We can't just erase gender. People think in gender, and they consequently speak it. I don't think twice about mentioning "some guy" commented on my post, for example. Just the other day I decided to be even and refer to a hypothetical person by using "s/he", and even got called out on it.

If either of you bothered to read the thread before moving forward with your agendas you would have the answers to the questions you're asking[1].

[1] https://news.ycombinator.com/item?id=12232822

Maybe because she had a female name?