Perhaps in a Kool-Aid drinking hearing about all this, the other line of argument needs to be made to get through to them.
Women will not accept transwomen in prison with them. Women in prison tend to have had difficult childhoods or early life, up to and including a history of being assaulted by men or otherwise disempowered by them in really big ways like physical assault.
Women in prison will, at the first whiff of a transwoman looking at them funny or "accidentally" touching them, gang up on the transwoman at the first opportunity. The result will be akin to that rabbit that killed a snake after it ate her babies.
Therefore transwomen will not be safe in women's prisons.
Prison doctors aren't likely to be ofé on medical management of trans issues (assuming, just for this line of argument, that any medical transitioners are the beneficiaries of this law).
They need to be housed in a wing to themselves in one prison, where the prison doctor can stay on top of all the extra stuff he or she needs to understand to manage a medical transition. Where natal female guards are not at risk of being overpowered by someone physically bigger than them who could then escape or get at the women.
Natal women should not be housed in the same cell as transwomen, but they shouldn't be housed in the same wing, either. For the safety of everyone involved. And this should be the case for anyone trying to get into a women's prison.
Of course natal women need protecting, but the people making this stupid new law don't care about that, so reframe it in terms they understand. Trans women will be at risk in women's prisons, too. And trans men will be at huge risk in men's prisons.