The game uses baked renders (they are not 3D scenes that can be manipulated in-game) so if I added a female protag that would easily double the filesize and triple my workload, and I'm a solo dev so I'm already stretched thin as it is :P
If by "play as a girl, regardless of sex" you mean will I add the ability to choose female pronouns, it's unlikely but depending on player demand it's possible. As with everything else, I have to balance "how much time will this take?" with "how much demand is there for it?" Currently, you're the only person who's asked for it so demand would appear to be low. But if more people request it, then I'll push it further up my list of "things to add" :)