You file Form W-7 if you need an ITIN (Individual Taxpayer
Identification Number). The IRS uses an ITIN for people who need to file
or be included on a U.S. tax return, but do not have, or are not
eligible to get a Social Security Number (SSN). If you want to file her on your return and file jointly you would file this form. I have put some helpful information below for you to read over. Let me know if you have any more questions.
https://ttlc.intuit.com/replies/3300174
https://ttlc.intuit.com/replies/4406181