Hi Great Aunt, and Welcome to Cruise-Chat!
I especially love silver jewelry - any suggestions where to go?
Just about everywhere! You should take your time and shop around and do some haggling. Visit several shops and vendors. Especially if you are looking for a particular piece. Silver prices are tricky while shopping down there.
I have bought a few pieces at Viva Mexico downtown. It is a slightly higher end store than those along the way, and has more of a selection than the vendors. They will negotiate and they take credit cards.
I haven't been on the Destiny in a long time and it was an Eastern cruise. For some reason the last several years I end up on Cozumel aboard a Carnival ship though.