How to prove jewelry was separate property and how to get it back.

Because this was a gift to you, technically the jewelry should be your separate property. Unfortunately, you will have to prove that your husband's mother gave that jewelry to you as a gift. Is she still alive? Do you have anything in writing where she refers to the jewelry that she gave you? Any evidence that you can produce to show that the jewelry was a gift to you from your husband's mother will be helpful. Absent that, you may potentially lose on your separate property claim.

Is your mother-in-law still alive? If she is, and she's called as a witness, what will she say about whether it was a gift to you? Does your husband acknowledge and admit that he's got the jewelry, or has it "disappeared"?

It may be difficult to get your jewelry back or receive the fair market value, if the jewelry does not exists, unless your husband's mother is still alive. Then, if she is alive, will she acknowledge that she gave you the jewelry?