I brought this up with @pinwizj back in January and was told then that he thought that as part of the rebuild process, the system does look for new players submitted in Women-only events and then updates their profiles to be Female.
@Shep makes reference to using genderize.io in this post: Supressed player
So while it defaults to Male, there is some effort put in to identify Female players as well.
But as has been raised, really the best person to be identifying their gender is the player, which can be done by registering (albeit in a binary manner). I made up a sheet to be displayed at our monthly tournament to explain to players how to register:
Feel free to use it at your own events!