No water bottles allowed?!? Should this be a rule??

My little sister just started middle school. We are in the same cluster of schools and she is going to my old middle school which is full of bullies, suicidal kids, unnecessary rules, and disrespectful teachers. She has a water bottle and she has been bringing it to school for the past week and a half that school has started. The third day of her bringing it they told her she wasn’t allowed to have it and the principle “wasn’t sure how she felt about water bottles” so they now make her put it in her locker. She has social anxiety and they apparently are only allowed at their lockers twice a day as a class and has issues opening her locker correctly when she feels rushed or under pressure. One of her teachers constantly gets mad at her and talks about her in front of her to other teachers in a rude tone about her bringing a water bottle and having issues with her locker. She follows their rules and puts her water bottle in her locker and gets it out only during lunch, however they have let other kids carry water bottles the whole day without being spoken to. I don’t see what the issue is with a water bottle and I feel like that is completely unnecessary and wrong. I carry a water bottle every day and has since I started school and am now a senior and have never had anything said to me. Should this be a rule?? I think this school is insane, they even have a thing called “freedom Friday” where kids are allowed outside for an allotted time only if they bring their agenda to school that day🧐🤷🏼‍♀️