Let her challenge stupid rules. I would bet they don't even know why they have such a rule other than for the sake of having one.
As for the theory it's good practice to abide by rules as if they get a job in a kitchen then they'll need to wear a hairnet - well that's a pile of crap too. A hairnet in a food production environment is an easily justifiable and understandable rule - not something arbitrary.
So would you let your child wear a nose stud, bright pink hair or a very short skirt?
Where would it end?
Some schools choose to have a ban piercings for health and safety reasons but some choose to do it for other reasons.
A uniform is there to ensure every child is treated equally, regardless of how much money their parents earn.
A school makes rules for whatever reason it chooses.
If you don’t like the rules, then find another school that fits with your beliefs.
If you can’t find one, then homeschool.
But whatever you do, don’t encourage your child to break a rule knowing that you as a parent won’t suffer the consequences - as that is shit parenting.