Maybe she just hadn't had her coffee yet.
I've given up on expecting courtesy or support of courtesy from other people, though I will continue to always be courteous. I've also made a personal project of not analyzing or allowing myself to be affected by people's little behaviors like this, but man, it can be an effort. Not claiming I've perfected it whatsoever. So I get it. I really do. Little encounters can stick with me if I let them swim around in my head. Step one: Try not to let things swim around. Put yourself in the next moment and stay on that track until something of more import/consequence comes along to occupy your mind.
It was morning, the place was busy, she was alone and probably zoning out or distracted. All factors that can make a person not think or respond at their best. At least she didn't snark at you. Point for her, right?