It wasn't. They'd had a busy day, with 2 guys out sick, and since my car wasn't urgent they put it at the bottom of the list and didn't get to it. To me this wasn't a big deal. It happens here, too.
But Mary decided to take a stand on my behalf, and told the guy that since this happened I shouldn't have to pay for the oil change. He agreed, and told her that if I bring it in again today they won't charge me for it.
Mary was so proud of herself. I didn't have the heart to tell her I bought the lifetime oil change for the car 12 years ago, and haven't paid for one since.