That could be seen as discrimination or preferential treatment, and your daughter is being "singled out" and treated like a "whistle blower."
Thus, she is harassed more.
The school... does nothing about it. That bully's Mom, is equally at fault....
MOST schools/Stateshave a zero-tolerance policy for bullying which ALSO includes any behavior from faculty and/or staff... and of course other kids.
Contact an Attorney. ANYTHING you correspond to the school about, put it in WRITING. DOCUMENT everything... since the inception of the incident as well.
Your daughter is being more than bullied... and she has a medically confirmed ADHD condition. She is being preyed on.
Me, I would NOT allow it to happen.
I would, contact a Lawyer.
It will not be solved by talking to them about it. They are ALL bullies. And they will continue to jerk you around... meanwhile, your daughter is targeted for daily mistreatment.
All the best,
Susan