I think my fiance should not wear jewelry she got from a past relationship on the day we are to be married.
Why don't you want her wearing jewelry from her first wedding?
This jewelry will remind me of her past husband
It is okay to wear things that are from other people but things that were part of her previous wedding is wrong. People will think it is inappropriate and talk.
Why would they think that?
People might think she is not over her past relationship if she wears jewelry from her ex to your wedding. I think it's fine if you ask her not to.