I might be a little hurt they had never been worn, but as you say, they are wildly inappropriate for your climate. In which case, I think its fine. Its kind of strange for her to be asking to have them back IMO. Selling them and giving the money in the piggy bank is a great idea.

I think if we kept everything we'd turn into crazy cat lady hoarders!
Im a crazy cat lady hoarder. I have 6, and thier cats, in my hallway cupboard right now.