If you have a penis, you ain't getting in.
I was going to agree with this, because castration seems very apt under these circumstances.
But then, I can think of many ways a rapist could intimidate women, without their penis.
So, personally, I think if you're born a man you stay in a male prison. Particularly if you have been convicted for sex offences or violence.
As far as I know, male prisons have separate accommodation for those who are both more vulnerable, and those who are more violent. To protect both themselves, and others.
I don't know if female prisons have the same? Obviously there are violent women, but there are fewer of them. Or maybe specifically in terms of inmates, the percentage is similar?
I'm wondering if male prisons are just set up better to accommodate violent people. In which case why would you ever send them to a female prison? It seems like a double whammy of stupidity.