Who says its a discrepancy? With the significant amount of time between petition filing and the submission of the ds160 people's lives and circumstances do change
Follow the instructions and start by paying mrv fee, fill out the ds160, schedule the interview & medical. Make sure she has all required documents ready. Your wasting time if you are doing nothing.
My fiancee didn't even have my divorce decree when she had her interview because the divorce decree is already in the petition itself. This is utterly strange. If you look at the list of required documents, the petitioner decree isn't even listed only the beneficiary's is required