I suggest you read twilight. that book contains everything you should never do with writing a female protagonist. and then read something much better like Kim Harrisson's Hollows books. Rachel Morgan is a badass bounty-hunter-witch-that-can-use-demon-magic, but isnt super serious and has some big flaws like always choosing boyfriends who are bad news (in vaious ways), never keeping out of trouble, and being a bit of a thrillseeker. Ivy, in contrast is a bad-ass, wealthy, self-assured, bi-sexual living vampire who was abused by her master and can't seperate blood drinking from sex or sex from love.
Also, just write a character. If in the proccess of discovering who that character is, you find out she just happens to be female, fine. If not... well you get the picture.