Witch is already female so writing female witch just looks silly.
Actually, traditionally witch has been a gender-neutral term. In fact, plenty of men were burned at the stake for being witches. I'm not sure when the term began being applied almost exclusively to women, but I'm guessing Macbeth had a lot to do with it...
It's like most people assuming "duder" applies to men only. It's gender-neutral just like "witch."
I dunno man, Merriam-Webster states that witch is a gendered term: http://www.merriam-webster.com/dictionary/witch
"Witch" is non-gendered according to Wiccan folks and they would probably know since they call themselves "Witches." (Also Duder Witch will now be my fan-parody game of Bullet Witch.)
Regardless, gender is actually a big theme of the Fantastic Witch Collective. Apparently it will touch on this sort of discussion.