This basically tells us that her old friend was a complete loser and a horrible person who decided to take out her own frustration on her friend. I still don't get why the MC would just decided to leave that school just because people stopped talking to her, and it's even worse that she just decided to let people ignore her instead of talking to anyone to clear up the misunderstanding. They did make her out to be a really shy person who puts the blame on herself though, so it is somewhat believable.