My daughter is 10 years old autistic and mostly nonverbal and she holds her hands over her ears when noises are too loud or when she's having a sensory overload I have some noise reduction headphones 🎧 that seems to help a lot

Well, that's probably because they hurt.
My Son was that way at first, but I developed a technique to help Him and all that you'll need to do after every bath/shower is this:
When he get's out from bathing you til his head to one side, Gently squeeze top and bottom, then push the back of the ear, then Gently pull the Ear-Lobe and then the back of the ear, and that helps clear anything from inside the ear (canal).
After a few times he will see that it benefits him and he'll be more acceptable to having it done.

He hates me touching his ears but I don’t see anything when I try to look!

Noise-Cancelling Headphones in need?
Do you clear His ears out after a Bath/Shower?