Is there a market where I can sell her custom-molded hearing aids?

97 beat me to it. I would just add, though, that you'd better have a quick look at your mother's repayment agreement and see what it says about this situation (given the market, the provider will be used to sorting things out with relatives of people who have passed away).

It must sting a lot that you're having to deal with this on top of losing your mother. My condolences on her passing.

Perhaps you could ask the place where you bought them if they know if they could be remolded for another person and what that charge would be. Then if you offer them for sale, you could pass that information along. Sort of a sales incentive.
I know that eyeglasses and hearing aids and other medical equipment is sometimes donated to various organizations but I'm not sure how you would go about selling them. I'm sure they would be priceless to someone who can't hear.
I'm sorry about the passing of your mom.