not knowing the first part of your itinerary, there are a couple scenarios that come to mind:
1- whatever you were doing in AAA (orig departure point) for however long you were there did not require a rental car, and you now need a one-day one-way rental from AAA to BBB (new departure point)
2- you have a rental car that you picked up at XXX (could be AAA) but you now have to return it to BBB rather than AAA

imo the likelihood of DL doing anything to help you in (1) is miniscule ... the impact under (2) may not be as big you think; $50 gas for a 90-mile trip seems rather a lot, although it's believable if you're looking at a per-mile charge as well

again, not knowing the first part of the itinerary, you could consider rerouting into BBB so you could both pick up and return the car at the same point (given the magnitude of the schedule change I'd think DL would be amenable to this if it works for you) ... iirc I did something similar a few years ago, changing a CMH booking to DAY when my connecting flights were re-timed from a 55-min layover in ATL to either an illegal 31 min or an exceptionally inconvenient 3+ hrs with a midnight arrival