William,
I kind of live by the "it is easier to beg for forgivness than get permission" In this case she asked for Permission and was told no. Then she willfully defyed the rules. That is why I am on the side of the school. Had she not asked, not thought about it and tied an Eagle feather on her cap that morning as a show of what ever, and the head master made a huge deal out of it. Then I would probably agree with you. I went to two different Private schools. They would hold your diploma till you cleared the drom. We had teachers that checked us before we went up and had a few spare robes and caps incase you modified yours to an unacceptable level. If you ruined the dorm or were unacceptable at graduation then the school held your diploma till any and all fines were paid. They also threatened to send a letter to revoke your transcript to the college you were planning on attending.
When I was at Military school I came back for a graduation and was asked to check some of the graduates uniforms and make sure they were not wearing Red socks, that they did not shave words in their hair....you get the point.
