I think this is the site that is quoted by the lady who sold the necklace in the image Q linked…

https://zinniafolkarts.com/blogs/news/36153281-what-do-milagros-mean

A lot of people picked up on the fact that it is an offering to the spirits but there was also this in there…

"People also might carry a milagro with them in order to get its benefit. For instance, a curandera - a spiritual healer - might bless a milagro and recommend that the person carry it in her pocketbook or on her person, in order to cure a physical ailment or to ward off evil, or bring about a change of fortune."

This seems like a more meaningful explanation for milagros on a necklace.