OP, it is tough for you, and tough for your dd. And probably also tough for Bob. Dont contact mum. Dont be angry with her. She probably needs the friendships of school mums more than she needs judgement. Very few parents will admit to others that their child has a problem.
We had 3 Bobs in first grade a couple of years ago. It was a small class of 15 kids, and 3 bobs. Each bob was on a mission to create more bobs, by distracting others and try get them to join them in mischief. We were worried that we would have 6 bobs if we did not turn the bobs into peaches and cream. At break time, bob1 would eventually also seek out bob4 in second grade, and bob 5 in third grade, who was also new to the school.
Our school took the view that these were potentially unhappy and insecure children with unstable homelives, and they needed all the help and support they could get from us in turning things around. Neither of these children trusted adults. They did not react well to being spoken to, they would hit, kick, spit, throw rocks at teachers.
We could not tell other parents anything about how we were dealing with the bobs. All we could do was try reassure the parents of other children that we were dealing with it but changes would not happen over night.
But what did we actually do?
The bobs became a focus on each weekly staff meeting. We addressed break time, lesson time and after school care, and allocated key people to each child. They key person would have a special focus on building relations and trust. Talk to the bob, show keen interest in bob, and let bob understand that they had at least one ally in school that was in their corner. TAs and also admin staff and leadership were important in this work, as they were present during both school, break time duty, and during after school care.
In class:
Learning partners and collaboration in class. Carousel where children were divided into small groups. The bobs were never in the same groups, and the groups were tailored especially with a view to who each bob got along with.
Social competence in class and role play.
More teachers on duty during breaktime, so there were always extra staff around the bobs.
Various measures were taking to address behaviour at each incident.
Time was spent talking to bob at each incident. Bob was guided into an understanding of their own behaviour, the effect on others, how the other party would view bob after the event. Focus was on making good choices and making agreements that this should not happen again. Our approach to bob was without anger. We asked carefully though through questions, and let them take time to answer.
It was not easy. These conversations could be challenging. Bob1 was mine. I knew we were starting to turn a corner when he told his mum that he knew he could always go to Ms Shadow if he needed somebody to talk to. We also took time to speak to our bobs when times were good, show them we cared, show them we liked them, valued them for all their good sides. The received a lot of praise when they were doing something good, and were whisked away swiftly for a talk in private to avoid them feeling ashamed in front of their class if they did something they shouldn't. Stern talks, anger and punitive consequences does not necessarily help bobs. It may force them into submission, but it will not help them.
The time we invested with the bobs, and also guiding their mums, paid off.
Today the bobs are happy and well liked children who are well integrated into their peer groups. All three of them are lovely children, and a joy to be with. Bob 4 is doing much better, and bob 5 is also doing great.
If school is fobbing you off saying there is nothing they could do, thats bollocks. It just takes time and effort and magic will not happen over night.
We have had many bobs, and in my opinion, school can only help the victims through helping the Bobs. Bobs matter. Their lives may not be great, and as teachers we have a duty to help our bobs.
But if the school is not willing to help, then change schools.