your wife is right. Who said NIW must file ETA750B?

USCIS said.

EB-2 Eligibility and Filing

EB-2 petitions must generally be accompanied by an approved, individual labor certification from the Department of Labor on Form ETA-750.

If you are a worker with exceptional ability in the sciences, arts, or business, you may apply to waive the requirement that you have a job offer if such a waiver would be in the national interest. To apply for a national interest waiver, you must submit Department of Labor Form ETA-750B.

http://www.uscis.gov/portal/site/uscis/menuitem.5af9bb95919f35e66f614176543f6d1a/?vgnextoid=3460194d3e88d010VgnVCM10000048f3d6a1RCRD&vgnextchannel=91919c7755cb9010VgnVCM10000045f3d6a1RCRD