Trans women are subjected to sexual violence from men in the same way that cis women are. They need to be protected from male violence.

All women in prison are at risk of sexual violence. That comes from other prisoners (including cis women), and from officers.

Focussing attention on the small number of trans prisoners, and ignoring the risk from cis prisoners and from staff, means that women will continue to be at risk of sexual violence.

Then, how about this. I understand the view of no segregation at all. That's just one big group, no additional work of separation. But how separation by biological sex more meaningful than separation by gender identity?