She has a hot spot, but tbh it's not that much hotter. If I put my hand under it it's only slightly warmer. I just figured since she seems to spend about equal amounts of time in the hidebox under the hotspot and the other hidebox on the opposite end of the enclosure that it was probably fine. But perhaps that is the problem, and she has just been lucky to have no vomited before.

What is the best way to make a warmer hotspot without significantly raising the ambient temp?

As for the stiffness, given that she is curled up now I'm thinking her belly likely hurt from the strain, and she just needed to rest. She is curled up normally and sleeping now.