Does sharing a lift mean staying through every movie credit?

The credits started, and my friend settled farther into her seat. 'There might be something right at the end,' she said. I had the car keys and was thinking about my dog waiting at home.

We'd agreed that I'd drive and she would buy the snacks. I hadn't mentioned an exact time to get home. She hadn't mentioned that she always stays until the screen goes dark.

I said I'd meet her outside. She looked hurt: 'We came together. It's only another few minutes.' I waited, but there was no extra scene. On the way back I complained about wasting time, which made the evening worse than the actual wait.

I don't want to rush her out of something she enjoys, and she doesn't want to be left alone watching names scroll past. How much of an outing should a shared ride decide, and what should we agree before the next cinema trip?