Today Was The Day One of Us Forgot to Wear Shoes

This morning the youngest member of the household, age 10 and a half, went to school without shoes. She forgot to put on shoes. Hm. Do I get mad or do I laugh? I couldn't help but laugh. Is it my fault I didn't make sure she had shoes when she left? Do I have to check for that? Did I think I had to check for that, with someone who is 10 and a half?
About two blocks from the school, she looked down at her feet, looking for her shoes so she could put them on. She looked down and around, and then covered her fingers over her mouth in quiet contemplation as we both realized what happened. She usually carries them from the house to the car, since she has a lot of tying to do and we're usually running late. We were already just barely going to make it on time. If I turned around to go back home with her to get the shoes, and brought her back to school, she would be at least 20 minutes late. I had to make a quick decision about which would be better, to be 20 minutes late with shoes, or on time and without shoes. I decided it would be better for her to be on time. She had black socks on, and long, black pants that covered her feet, so I thought perhaps she could inconspicuously go to her classroom, and I could go home and bring her shoes back to the school. When I got back to the school, about 15 minutes later, I brought the shoes in with a bag, along with her clarinet, which she had also mistakenly left behind (in the car, though, and not at home). The school secretary called for her to come down and pick up the package. When she came down, I whispered to her, "Did anyone notice?" She said, "Yes, as soon as I walked into the classroom, the teacher yelled, 'Where are your shoes?'" A few of her classmates laughed at her and questioned her, but when she recounted it to me later, she seemed unfazed. What would you have done?