Whoa, I thought.
Maybe this is going really well. She hasn't switched to English. Rock on. Dang, I'm doing well today.
Then, as I was ready to pay, she told me that my German was good.
She said that she wasn't sure if I wanted to speak English or not but figured that I must have wanted to practice my German so she continued in German.
[Though I am thankful for her kindness and thoughtfulness, I am sad that my German is still so weak that people's first thought is to switch to English.]