I can just see it.. Or aurora. ^^

she had ALOT of time on her hands for years

Considering Rapunzel is generally an artistic person with a tendency to learn fast and effectively advance her skills in various areas, especially since she already has an experience with playing a musical instrument (guitar), being the only DP to have this kind of experience at all, I'm sure she is the one most suitable for that. Also, personally, I can't help but love a "fanon" idea of Belle playing the piano, for some reason it seems like something her patient and diligent self would be able to learn and enjoy doing.

I think it's more her style

Also Belle and Aurora.

Most of 'em would. For a good wife, (not necessary, but a good point) back then playing the violin would help ladies such as Mulan. But i'm not sure if they had violins back then XD, Rapunzel? Not a CLASSICAL instrument. She does play the guitar though. Aurora has everything to do with grace, and Belle would do many things for fun. Mermaids were thought to be great with instruments back then.

I can actually visualise Rapunzel playing piano or a violin.

Or Aurora

She had a lot of time up in that tower and does she play an instrument during "when will my life begin"?

I can see her playing piano. She probably did when her father was alive.

Love these icons :)