Yep, sounds like this has gone way beyond normal kid behaviour, particularly the notes and biting. DD1 has a girl at school who has been causing her grief and I have been speaking to her teacher, who is already aware of the issue. I haven't raised it with the mum because it hasn't gone too far.

Notes and biting are a form of bullying that the school MUST do something about about. Photos and the note need to be taken to their teacher so they can be made aware of it. Schools do have a duty of care for the students from the moment they leave the parents til they return to them, so issues on the bus is a school related issue.

I would suggest raising the issue with the school, see if they are aware of it and find out if they are doing anything about it. If not, ask what will be done, and if you want, ask for a mediated meeting with the other mum, particularly if she is a nasty piece of work herself. That way you have documented proof of what is said in the meeting and it is kept civil.

This way it is being done 'by the book' and the other parent can't complain. With your DD, give her lots of positive encouragement to find other friends who play with her nicely and are always kind to her, not ones that scare her. We are working on that with DD1, and she has made some lovely other friends, but until they swap classes next year, she still has to deal with her.

Lots of hugs to your DD