Rare as female werewolves are in the world of television and film it is difficult to say with any authority what the proper term (if any exists) for one might be. However, in my experience, both of the terms werewolf and shewolf are acceptable.

However, it possible to arrive at a gender specific (feminine) term based on (one of) the accepted etymology of the term werewolf. The term werewolf is thought to be derived from the Old English words wer (or were) and wulf. The later is clearly the ancestor word of the Modern English wolf, though it could also be used to describe a beast. The Old English word wer is a gender specific term for a male human. The Old English word mann (or man) being a gender non-specific (i.e. equivalent to the Modern English human). Hence the term werewolf literally means 'manwolf' or 'manbeast'.

Assuming a similar pattern of etymology, it stands to reason that the Old Englsih word wif, a gender specific term referring to a female human, should be invoked when referring to a female 'werewolf'. However, wif is thought to be the common root of the Modern English words wife and woman (only the word fragment woin the later case). So the correct terminology for a female 'werewolf' could arguably be either wifwolf or wowolf (if one accepts the corrupted woover the uncorrupted wif, which has come to refer to married women only).