Hmmm. Well the fact that they're both on the hot side could explain why. Perhaps your snake feels that it needs to be close to a hide, but doesn't want to be really warm so is hanging out on top of the hide where it would be cooler but is still close to the hide in case it should need to hide.
The only two things I could tell you to do is perhaps downsize the rock hide (looks a bit big for your snake in the pictures) and add another one that's the same on the cool end, to see if she likes that better. Balls are funny and they'll pick favorite hides for no apparent reason, so it's best that you have at least one matching pair of hides.