DrBeeper, sorry to hear about your loss.

Don't have too much useful information for you, but AA does have bereavement compassion fares available, generally for reservations within 24 hours (or less) of departure. When I've had to use them, they're generally at least 60% off the full fare (sometimes less), and have no real restrictions. Call AA reservations at the numbers tom911 listed above, or the number listed on the back of your card as soon as you can.

It is technically possible for UA to transfer the ticket over to AA, though I would doubt that would actually happen. Doesn't hurt to try though.