My wife is out of the country until February and her residents card expires in March. Would it be cutting it too short to file the I 751 about a month before residents card expiration? I'm assuming that as long as you file within the 90 day window that you're okay?? Thanks for your help. One other quick question. She already submitted biometrics during the AOS. Does she have to to it again? If so, how long does it generally take after submission of the i 751 to have the biometrics appointment? Thanks again.

You can't file BEFORE the 90 days ... anytime within the 90 days is fine, but you're going to want to do it so you get the NOA1 by the time the green card expires I'd assume, as the NOA1 is also an extension of her green card, valid for 1 year.

Biometrics will be done again.

Yes she will have to do her Biometrics again, an appointment letter will be sent to her once she submits her application.