My wife's name on her H-4 Visa has FNU as her first name (while her "given name" on the passport is labelled as "last name" on the Visa). I am applying for her ITIN and confused about the 1a and 1b sections of W-7 form.

1a - states to enter legal name as it appers on your document.
1b - Enter you name as it appears on your birth certificate.

So should I fill "FNU" name in "1a" and passport name in "1b" ? Her passport name is same as her birth certificate so if I fill 1b with her passport name do I need to provide a copy of her birth certificate ?