There have been some excellent suggestions given here!
I have a very different angle which is …hard. I obviously don’t know the whole picture, but it sounds like your daughter is not going to be able to be independent in the shower for a long time (maybe even life). If I’m correct, this is the same boat our youngest daughter is in.
She too has always been very private (we still laugh about her telling her daddy to turn around from her little towel-wrapped self when she was only 2!!). She requires assistance into & out of the bathtub. Showering is not an option. She also requires extensive time to put medical bandages on ~90% of her body before being able to get dressed… which I realize is incredibly unique. All that to say, we’ve had to have lengthy discussions with our daughter as she’s gotten older & her disease has progressed. Both her dad & I need to be able to help her… which is another level of hard, and requires a lot of trust. We do everything in our power to make sure she feels safe with us, but that doesn’t always mean she’s “comfortable” with the situation. We’ve also had frank discussions with her, asking if she’d prefer a female nurse be hired to help her- but that would require being vulnerable & trusting a total stranger. At the end of the day, she’d rather those times be with us- where she knows she’s 100% safe, even though she won’t be 100% comfortable… I hope that makes sense.
All that said, let me reiterate that I do not know your situation & only you know what your daughter needs to be safe. I’m just sharing what we’ve done when we knew that independence was not a safe option for our daughter during bathing. We still respect her privacy & are as professional & protective as possible… but her safety & medical care comes first.
Best wishes as you manage your daughter’s safety & wellbeing!!