three months, so she won't get ticketed. You'll probably have to pay a registration late fee when you get the emissions test but at least she can continue to drive the vehicle.

Title 46.2-646
E. No law-enforcement officer shall stop a motor vehicle due to an expired registration sticker prior to the first day of the fourth month after the original expiration date. No evidence discovered or obtained as the result of a stop in violation of this subsection, including evidence discovered or obtained with the operator's consent, shall be admissible in any trial, hearing, or other proceeding.