Fenixp: The transformation is so brutal few PEOPLE survive it. I think mages were just sort of scared of murdering female kids as well as male ones... HOWEVER there WAS a female who received Witcher training in her childhood, but she was lacking mutation (that means nearly no potions since they are highly toxic for human and no above human reflexes), still, she was an AMAZING fighter and, to add up, she was able to harness magic. She would totally make an amazing playable character.
Stuff: She would indeed. My Lady is an avid gamer and we usually play two games using different characters . . . playing our separate games as time allows. She's an RPG fan and really tried to get into the Witcher. Not having a female character made the game less than enjoyable for her.
She played a couple of levels and just stopped waiting on me to finish my play through so we could move on to another game. Having the character you described above would have made the game awesome for her I believe . . . =)
I'm towards the end of the second book, and there are only around 5 Witchers left in the world and they are all men. It's revealed in the back story that an army attacked their castle and killed most of the Witchers and killed the sorcerers who were in charge on mutating the young children. The 5 remaining Witchers have no idea how to mutate new children, that's why the girl Fenixp mentioned was only trained in survival and sword techniques.
Maybe tell your girlfriend about the books, so far the first 2 have been translated into English. There are some great female characters in them, like Yennefer. She hasn't shown up in the video game yet though. Oh, and the video game actually takes place 10 years after the final book in the series. I wish the publisher would hurray up and get the rest translated.
So why can't your girlfriend enjoy playing a game as a guy character? I've played several games where the lead was female, and in RPGs I make some crazy cool gals for my party.