Currently the value is not very significant ($71 per share). But it is nothing to sneeze at either. They are owned as joint tenants (each person has a joint right to the whole just handing over half is not sufficient to fix this) and each person has a right of survivorship (if one dies the stock passes to the other automatically).
She should check with the broker about the value and number of stocks she owns. Depending on when in 1993 the stock was bought you have either 40 ($2840) or 80 ($5680) shares of stock (there was a split in Feb. 1993 and Mar. 1999). It is possible that she just has old certificates and ex sold the stock long ago and that is why the stock is not in the divorce.
Walmart pays a dividend; has she been receiving these payments (another $300 to $900 very rough estimate)? If the stock is good she should find out about getting these past payments.
If the stock is valid; then, she should take her divorce papers to a competent attorney for a consultation. There is a bit of money here, if valid, and the right thing to do would be to find him and come to some agreement (if you are correct and they were inadvertently left out of the divorce). When money is involve taxes tend to come into the mix, get good tax advice before any sell. (also realize that if you sell them and attempt to keep the money he might get tipped off come tax time and that could really bite you - just so you know)
If the stock is not valid you still might be able to sell the certificate to a collector. You also will want to check when the stocks were sold and if it was after the divorce; then, consult with an attorney regarding contempt (pros and cons).
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