I'm not making a point really, but I can think of at least 2 female serial killers off the top of my head: Rosemary West and Myra Hindley. However there was also a man involved in both their cases.

I don't know the rates for serial killers, but for murder/manslaughter in general in the UK, I think it's more like 90% male and 10% female perpetrators.

Bagpuss