Promise is a promise (?)

Five students from an all-girls secondary school had their heads shaved at the
charity event Hair for Hope in support of children with cancer, but were reprimanded
for breaking school rules on shaved or 'unfeminine' hairstyles.

Some educators and parents supported the school principal by saying that
she is well within her rights to chastise her students since they made a promise to her to wear wigs at school.

I disagree.

What the girls did was commendable -- why were they made to make that promise
in the first place?

Here's one solution in which the girls can show their empathy for cancer patients,
and still pacify their principal:

Promise is a promise (?), Part 2

It takes the Education Minister to finally knock some sense into the principal's head: