When you take her out of the water dish, do you see anything in the water bowl that looks like pepper flakes? If so, then she is soaking because she has mites.

If you feed her a large meal, she may be soaking because she's trying to relieve the pressure in her belly.

If you don't have adequate hides, she's in her water dish to feel something touching her on all sides.

If it's too hot in her enclosure, she may be soaking to cool off. How are you measuring her temps (stick on dial, strip or a digital thermometer)?