I've been waiting to get this back to you, but the grades just finally came in. So, she got the problem wrong, but the teacher added this comment:

"Hi DD, I appreciate that you prefer to think of the problem in equation form. However, part of learning is trying to understand things in another way. Curriculum asks students to do this frequently in the course. Please do the best you can to try, even struggle, with the models and questions that you are given.

Great job with your equation representation. You did an excellent job of explaining your thinking!"

To be honest, this is some thoughtful and kind feedback. I still think the model thing is silly, but I can't argue with "you're being asked to think this way, so TRY."

Edited to add: she actually got 4 of 6 points on that question.