You hit the nail on the head. In retrospect, I think it was a combination of the following two things:
Don't be pedantic. This is not a teachable moment.
Don't tell me to figure out a new module.
with emphasis on the former. In the end, the code worked and she could go on vacation with a clear conscience. She may have learned something, but to be honest I think I learned more. This reminded me that not every moment is "a teachable moment" and no matter how much I may want to, doing so may only succeed in limiting the number of teachable moments in the future.