Female Witchers were called... witchers, not very exciting but that's how it was. They were not common though as girls tended to die much more frequently during the trials (and survival amongst boys were already horrifically low). Those that did survive tended to be so horrifically mutated that they were not capable of functioning in human society. This of course meant that all the schools stopped even attempting to make witchers out of girls long before the time period of the books.
Sorry for going all puritan nerd, the art is very nice. I like it.
It was a very short segment in the Saga where Triss and the remaining witchers have a short discussion about the side effects of the witcher mutagens on the female body (nothing too explicit or in depth though).
This was than expanded on in the PnP roleplay where they went into some more gruesome details about it.
Though I suppose one could argue whether anything not in the novels or said by Sapkowski himself can be truly canon...