Hiding in water bowl is usuall one of three things.

1. Mites
2. Too hot
3. Safety/security issues

If you're sure it's not mites or heat, from the looks of the open and exposed tub, I would guess she's trying to hide. Even in a low traffic area, there's going to be a ton of light streaming in there and she may not feel closed in like she wants to.

Put a hide in there that she can fit in, even if it takes up half the tub. See if she leaves the water for the hide.