Also like to add some here, you need notarized copy of her passport and your marriage certificate with the form and send it to IRS. I think first you apply for ITIN and then you file tax return. But not sure now a days, because I did this 7 years ago. Anyway, it took me to 2-3 moths to get ITIN for her.
go to Irs.gov and in search box type ITIN or W7. One thing is for sure, you save heck lot of money filing married jointly. Good luck