Divorce and remarriage under USCIS -- sponsoring another spouse:
In family processing, with a USC spouse, as long as the immigrant arrived on a valid visa (and can prove this -- inability to prove this is a mess and the subject of much consternation, gnashing of teeth and occasionally litigation), her overstay will not impact filing during the I-130/I-485 process. She is at risk, of course, of getting tossed out on her "behind" PRIOR to the filing of the I-130. However, once the I-130 is floated in the system, she is fine (from a deportation standpoint). Be sure to file the I-130, I-765, and I-131 along with the I-485. That's a work permit (I-765) and advanced parole granting the right to leave the country (and return!) during the pendency of the adjustment process (I-131).