You should copyright your design to protect your concept. This would afford you some protections against others using it without your permission.
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I am not sure that you will be able to get a great answer on this site. The issue being that Avvo only has lawyers who practice within the U.S. and, since the silversmith lives and conducts business in Canada, U.S. copyright law would not apply in this case.
Since the U.S. and Canada are both members of the Berne Convention international treaty, this should be the governing law. Unluckily I am not familiar with the Berne Convention and am not able to tell you what legal recourse you would have against her. Hopefully someone on here will be able to provide a little more guidance on the Berne Convention and how it would apply to your case.
If you are still looking for answers, and no one else is able to help you on Avvo, I would recommend finding a copyright attorney who specializes in international copyright law to meet with and discuss your issue.
Answering of your question is merely general advice and does not constitute legal advice. None of the statements or implications made by this answer creates an attorney-client relationship with the attorney answering the question. The statements made in this answer are not to be solely relied upon and you should meet with a competent attorney to discuss any concerns you may have regarding this answer.
A copyright gives its owner the right to exclude others from profiting from sale or distribution of the work in the territory where the right is recognized.
Since the design is yours and reduced to tangible form (your drawings) you already have a copyright interest in it. The actual ring would be a derivative work. Design patent protection in the US is relatively inexpensive and should also be available to you.
With such protection in place, you would at least be able to restrict importation of rings using your design into the USA.
Consider meeting with a local IP attorney who can help you put the appropriate protection in place, and also draw up a contract for execution by the silversmith acknowledging the ring to be a work made for hire, conveying all rights to you, and agreeing to sign whatever agreements you require to document those rights (in case she adds something to the design that is separately recognizable as an original work of authorship under the copyright laws of the US).