We just found out that my wife meets the public service loan forgiveness criteria.  However, all the direct plus loans we have were made under my name (husband).  How do I apply her public service to our parent loan?

Not possible, unfortunately!

Thank you.

So if my wife had sat down at the keyboard and filled out the application instead of me, this would not be an issue?  You are not given an option (as far as I know) to add a spouse when applying.  I understand that the loan is not income based, but the only way I can pay it back is with our combined income.