How bad is her belly? A photo may help
Personally, I left the water dish out until I was there to supervise when dealing with my thermal burn snake... I also wanted to avoid him drinking too much contaminated water. But his was severe and he needed daily chlorhex at first às well as the soaks. Hydration was not really an issue.
With the cream, if you are using it daily, you will still want to remove the layer from the day before. A short soak helps with that. Use the water to gently flush away the cream and then you can give a short soak to allow her time to drink.
If her belly is only a little red after the shed, it may not be too bad. But if the burn happened while she was already in shed, she may go into another shed cycles very quickly and the belly will look much worse after.
The damage may still be under the skin where you can't see it yet while the tissue dies.