Is there any chance what you are seeing isn't bad shed but actual skin?
The reason I ask is you say she's been repeatedly rubbing that spot on her head, is it possible she actually rubbed off the scales in that spot trying to shed, and now it bothers her?
I've never seen a shed that would not come off when it got wet, that also makes me wonder if it could be a spot where she rubbed off her scales and you are seeing her skin.
If that is the problem, it should go back to normal after she sheds again, but do remove or at least cover the wood she keeps rubbing on, or it will just happen all over again.
Gale