So do you not have a basking bulb? You should have a lamp that provides UVB, and a lamp that provides a visible light and heat.
80-90 isn't hot enough to facilitate digestion. They need to be able to bask in at lest 95 degrees at a minimum for basic metabolic functions.
Heat rocks are also generally not a good idea. They need overhead heat, that is what they search out and is whats natural for them. Heat rocks also pose the risk of serious burns.
This girl needs all the help she can get, so the best thing you can do right now is make sure you are providing her as prfct of husbandry as you can.
This means a good
uvb bulb. The reptisun 10.0 tube or the arcadia 12%/14% tubes are great. Please note these are long flourescent tubes, not bulbs that fit into a standard socket.
You also need to have a basking bulb alongside the uvb tube which provides a bright white light, and gives you a basking surface temperature of 95-100 for an adult. If you have a large tank and large basking surface, I would shoot for 95-105, that way she can pick the temperature she wants.
Which leads into the next most important thing you need, a proper thermometer. No dial stick ons, you need either a digital with probe end, or an IR temp gun.
I know it can be a little overwhelming at first, but once you get all this stuff settled, it gets much easier.
Proper temperatures and husbandry are paramount for her right now, since her ailment is largely to do with the digestive system. And nothing is more important to the digestive system than proper lighting and heat.
-Brandon