I’ve only heard of a few female perpetrators of sex crimes against children in my entire life.
There is, of course, Mary Kay Letourneau, who seduced a 13-year-old male student.
And there was a case several years ago of a Canadian(?) woman who helped her husband abduct, molest and torture teenage girls.
However, I’ve never in my life heard of a woman who, on her own, was accused/convicted of molesting one or more children. I exclude Ms. Letourneau on the grounds that her victim seems to have consented (I know that 13-year-olds can’t give informed consent); he’s now in his twenties and still seems very much in love with her. Though the whole situation is weird and sick, her relationship with that boy isn’t quite the same thing as luring a child into a back room and threatening, coercing or forcing them into sexual acts. Which is what most of us think of when we think of child molesting.
I can’t provide a cite, because I don’t remember her name, but I do recall a case where a baby-sitter (woman) sexually abused a toddler girl to the extent that the girl’s genitalia were damaged enough that she could never have children.
Number’s wise, I’d say that there appear to be fewer as people are much more suspicious of men then of women, so people don’t make connections in children’s behavior after the event. I’m just guessing on that one, but it seems reasonable. Plus, more men then women are convicted of most crimes, like I heard that many female murders are never brought to justice simply because no one believed that a woman could do it.