i honestly disagree with wat some of u were saying because i got bullied wen i were growing up i had suicidal thoughts & didn't know wat to do i tried to tell a teacher but the kids lied about it & since i were a bad ass growing up the teachers mostly believed them i tried ignoring them but it didn't stop them from messing with me i even tried killing them with kindness but it only made it worst so i finally stood up for myself and that's wen it all ended so i think your sister should stand up for herself btw i know i misspelled alot of words lol
One thing I'd like you to remind her is that things get better and the others just don't get her. It also helps to have a spot where you can just think
You need to talk to your mons. Victims of bullies will have low self esteem, low confidence, and will have a poor personal view. Bullying gets out of hand and she mighy self inflict pain on herself. Please have your mother talk to the principal before it is too late.