Just to clarify...the 1099R has HIS name on it with HER SSN?
Or did she get some of his retirement through a QDRO and the 1099R was issued to her and she failed to bring it to you?

You should be able to call the bank that issued the 1099R, if its in her SSN, they will give you a copy....but first, you will want to ask her for a copy of the divorce papers so you can see what might have actually happened and you need to ask her  Did she get this money?   Did it get rolled into her own retirement account or some other type of account maybe?