It seems like the overhead heat is having trouble penetrating some of the decorations in the enclosure if the ambient is that much higher than the ground. I would get UTH on warm side. If you have the substrate super thick, it may take a good long while to notice any change on the surface if at all so take it slow adjusting it and have a thermostat based on the bottom in case of burrowing.

As far as swapping from mice to rats, my best advice is to be patient. Refusing a meal multiple times might happen, but eventually most of them will take the rat when they are hungry enough. Without a picture, it's hard to know what kind of shape she is in, but usually they can go a few months with no issue by the time they are that length.