What is this hypothetical trans prisoner in prison for?
Doesn't matter.
What is their risk status?
Doesn't matter.
And this is the problem with the risk assessments used to put them there. It's not about the man. It's about the women.
Virtually all women in prison have experienced male violence, and a significant number will have a lasting trauma response to men simply because they are men. It doesn't matter how 'safe' the man may be in theory, it is inhumane to subject women to constant fear simply to appease men who want to be there - for whatever reason. Women in prison are entitled to psychological as well as physical safety. And to dignity. This has been understood for 2 centuries.
Many men in prison are vulnerable - old men, young men, small men, disabled men... That's no reason to put them in the women's estate. My DP is kind, gentle, slightly built, wouldn't dream of attacking anybody, I've never heard him so much as raise his voice (except to be heard when we're on different floors) and he's about the last person I could imagine ending up in prison, but if he were caught up in something like the Post Office mess and ended up in prison for an entirely non-violent offence he shouldn't be in the women's estate. Because he is a man.
And doing someone's hair is about the most primal gift there is. All primates do it.