Delta has a customer service plan that references passengers getting bumped. That plan says "If there are not enough volunteers, we will deny boarding according to our boarding priority rules." But from what I can tell the actual order is not published. Usually they will bump passengers on the lowest fare, have no elite status, and/or checking in the latest.
Delta is has historically been the best as far as offering big vouchers to get enough volunteers. But if I was her, I would check in right at 24 hours before the flight. Her being on a basic fare and no status would definitely make her odds of getting bumped higher than many of the other passengers who bought a higher fare or has status.