Just be a good customer. You'll see, in time, that her attitude will soften, and things will be comfortable again.
It's hard to run a business, whether it's a startup or a breakfast spot. There are lots of stresses your customers will never see, and a lot of burdens. Especially financial burdens on non-venture-funded/bootstrapped businesses like the breakfast place. Maybe she snapped, maybe she overreacted. Maybe there's more to it than you realize. Maybe she gets annoyed with people who are too exacting about small financial things.
It doesn't matter. Just be a good customer to her. It's he best thing you can do.