She probably knew that she was just a rude person. I waited tables for a few years, and encountered similiar situations where one person out of a party was a total jerk, while the rest were perfectly nice.
You left a nice tip, so i'm sure she realizes that you weren't agreeing with the aunts behavior. It's nice that you realize it wasn't the waitresses fault. Waiting tables is a really hard job, and people like that are the reason. Once I had a man eat an entire order of wings, THEN complain they were too small and he wanted to be refunded.......?? After I had asked a few times how everything was. He himself had a $50 tab, and after waiting on him and his friends for over an hour, left me no tip.
In the future if this ever happens again, just be sure that YOU say thank you as much as possible, the waiter/waitress will appreciate your good manners :)