Update:

My wife got the attested copy of passport (page with picture and the page with Next to Kin information, photocopied in the same side of A4 size paper) from the Ministry of Foreign Affairs, Department of Consular Services, Tripureshwor, Kathmandu. They take Rs. 200 per page.
I submitted it to IRS along with my tax refund papers.
Recently I received a mail from IRS with her ITIN number.
They also sent back the attested copy of Passport.
Hope this information will help somebody in future...

Thanks,
TTT