There is a link on the nwa.com website to send in correspondence via email.
Here is the link:
https://www.nwa.com/talk/ttu.html
Be sure and list specifics, Name, worldperk number, flight numbers, specific issue your wife encountered.
Be sure and specify what you feel NW should do to rectify the problem, i.e. bonus points, ECV, free ticket, intl unpgrade certificates.
If you complain but don't ask for specific compensation you may just get a "were sorry" and "hope to see you soon" reply
Good Luck
RC