You can probably get the bank to at least let you view the contents of the box pursuant to the following statute:
655.935 Search procedure on death of lessee.—If satisfactory proof of the death of the lessee is presented, a lessor shall permit the person named in a court order for that purpose, or if no order has been served upon the lessor, the spouse, a parent, an adult descendant, or a person named as a personal representative in a copy of a purported will produced by such person, to open and examine the contents of a safe-deposit box leased or coleased by a decedent, or any documents delivered by a decedent for safekeeping, in the presence of an officer of the lessor.
(1) If requested by such person, the lessor shall remove and deliver only:
(a) Any writing purporting to be a will of the decedent, to the court having probate jurisdiction in the county in which the financial institution is located.
(b) Any writing purporting to be a deed to a burial plot or to give burial instructions, to the person making the request for a search.
(c) Any document purporting to be an insurance policy on the life of the decedent, to the beneficiary named therein.
(2) The officer of the lessor shall make a complete copy of any document removed and delivered pursuant to this section and place that copy, together with a memorandum of delivery identifying the name of the officer, the person to whom the document was delivered, the purported relationship of the person to whom the document was delivered, and the date of delivery, in the safe-deposit box leased or coleased by the decedent.
(3) The lessor may charge reasonable fees to cover costs incurred pursuant to this section.
(4) Access granted pursuant to this section is not considered the initial opening of the safe-deposit box pursuant to s. 733.6065.
Then at least you will know if your jewelry is actually in the box. If it is, then I think the easiest way to gain access to the box is either by doing a Disposition of Personal Property without Administration or a Summary Administration, naming the contents of the box as the asset passing to you (assuming you are the beneficiary of your mother's estate). I believe you can get forms for both of these types of administration from the court.
you should contact a lawyer to assist you. unfortunately it appears from the information provided that you will need to file a petition for summary administration seeking the contents of the safety deposit box. you will need to have any other sibling consent. by providing all details and documents to a probate lawyer he or she will be able to provide you better guidance.
without a detailed review by a lawyer can all the issues raised in your question be appropriately addressed...nothing in this response should be construed as establishing a lawyer client relationship..the answers herein are for informational purposes and not to be construed as advice