airport agent refused to apply me OU voucher to someone else's ticket...

I canceled a TYP ticket, got the credit, and put a new reservation on hold at aa.com. the new reservation is for me and my daughter.

I went to airport and applied the credit to my ticket. done and got residual $660 something as OU voucher. and the agent was very firm I couldn't use the voucher for anyone else. I was completely lost and decided to come back and do more research in case she was right. from people say here, seems she was wrong? should I try going to airport again, and hope another agent won't be as clueless? or should I just mail in the voucher? it's $660 and new ticket only $240, so I have to mail in, and wait for balance to be mailed back again?