Hello, the wife's mother can file for her and both application can be concurrent, because you can have two application with the USCIS. As soon as one is ready to be adjudicated, you'll withdrawal one. I had to withdrawal my green card renewal application because my naturalization was adjudicated before the green card extension was. This happened because I joined the military, while I was at my citizenship interview, I had to write a withdrawal letter same day, so I can become a citizen. I hope this will help you. Cheers