I’m worried my daughter is being bullied again

My daughter was bullied this time last year. Her friendship group turned on her after she had an argument with one of the main girls. It was very difficult to watch, as a parent, and my husband and I were very worried about her. They isolated her and said very hurtful things on social media about her. She was so frightened of them that she used to eat her lunch in the toilet. Her school did nothing to help and we really struggled as a family. Her mood deteriorated and she even stopped eating. I was bullied as a child and I still feel the pain of it all. My husband was very concerned about her, so we moved her to a new school this year and everything was going very well. She has made a new group of friends, who are very supportive and she was happy again. But, recently, I have noticed that her mood has started to dip and she has stopped talking to us and I’m worried all over again. Can you please give me some advice?