I won't claim to be eloquent, but even just a short note - all they need is to get the gist that you support them in supporting women's rights - something like:
'Thank you for your recent comments on the subject of males in women's prisons. It's good to see politicians standing up for the protection of women, who should never be incarcerated with males. Women prisoners are often vulnerable and deserve our support and compassion. Their loss of freedom is punishment enough; incarcerating women with males is contrary to the Geneva Convention and puts them at risk of both physical and mental trauma.
I'm sure you'll agree that women's rights are human rights, and that women deserve to be protected from the threat of male violence. '
Maybe someone else could improve on that - I have to run for the school pick up!