I have done some research into the female killers in horror movies on the internet to show that there are examples of them and they do work well. They are even on some of the most influential horror films of all time.
Mrs Pamela Voorhees Friday the 13th (Original) (Sean S. Cunningham, 1980)
Tiffany from Bride of Chucky (Ronny Yu, 1998)
Samara from The Ring (Gore Verbinski, 2002)
Debbie Salt from Scream 2 (Wes Craven, 1997)
Using these female killers as evidence that it works and isn't always just male killers. We have used aspects of these killers and implemented them into our film for greater effect.