Some school faculty and administration are incredibly petty and vindictive. Certainly not all but a lot. Grown adults absolutely pick favorites, bully students, talk down to them, and carry out petty beefs for any reason or no reason at all. Sometimes they hurt the children to get back at parents they don't like. Sometimes they (for whatever reason) seek validation from students and will participate in bullying of unpopular students. These can be trivial things, like accepting late work from some students but no others or grading one student's work more harshly. Other times they believe they are doing a student good by "teaching them a lesson" or expressing their disapproval of the student or family's lifestyle.
I have absolutely no problem believing the school administration and coach were offended and rather than discussing it with the 14 year old they decided to prove who was boss by punishing her.