My guess is 90F is a little hot for her on the hot side, but I don't know that for sure. I would imagine 86F is probably a good hot spot. However, ambient seems okay.
Is she eating? Have you ruled out mites? Does she have appropriates sized hides and on the hot and cool sides? It might not be a water issue, but rather, a safety issue. I think I recall seeing a picture of her in the jar and she looked pretty tight.
The only time I see my corn snakes in the water bowl is when it gets too hot (in the summer) and I have to adjust the thermostat down. If the ambient gets above 82F, they are not happy. They go right in the water bowl to try and cool off. However, I am guessing that isn't your problem.
How are you checking temps?