There is a recent thread here in which JonNYC posts AA's current rebooking OA policy.

This would seem to fit the bill for rebooking, e.g. OWE in F facing an overnight delay. What I can't answer is whether AA's IRROPS interline agreement with UA does permit it to reissue from what would be a coterminal for AA but that might not be the case.

Only way to have dealt with this would have been to politely thank the agent, say you want to think for a minute and then walk over to some other agent.