I realize your post is 12 years old, and there were no replies ever. But, I was wondering if your wife was successful in tracking down her birth certificate?
Yesterday, I discovered the name of a possible relative in the list of Russia's Fallen. It said he was born in 1924 (no month or date) in Dnepropetrovsk. I was hoping to track his family backwards to see if I can find a connection. But, have no idea on how to find a Soviet birth certificate.