Ah haha, sorry I haven't logged in for awhile. Did you get Roxy to eat yet?
As long as there is enough room for the snake and the rat inside the hide (everyone touching the ground), there's enough room for her to eat it. I can't speak for the exact size of the hide, or your snake, but it should be alright.
For the heating thing... I have to admit, I don't aim for a specific temperature. I just leave the hot water bottle on for a few hours. It's probably over the recommended temp, but I figure it's only one day a week.
I also forgot to mention. Stay with slightly undersized rats if your ball won't eat the larger ones. Mine definitely gets intimidated by the big ratties![]()