Thank you for your post bloom3 and I agree ignoring/not reponding does work for many bullying situations. The mother gave the finger to my 13 yr old 3 times and we didn't do anything - daughter just stood there. The straw that broke the camels back was when she did it to my 9 yr old. In my mind my 13 yr old can handle herself - she a brown belt in karate and is as tall as the mother - she's stronger in my mind. But it's scary and intimating for my 9 yr old to be getting off the bus, walking to the house and have the mother do this. This is direct intimidation of a child. Not 2 kids who are having a problem, but a grown woman behaving in an intimidating way to a child.
Since she didn't appear to be backing down, even though we weren't responding, I made the decision to ask the police, what to do. They told me, this isn't something to let slide and they wanted to go to her house and give her a warning and they did.
Yesterday there was a surprising turn around by the family. Their daughter came to school and gave my daughter a nice card, friendship bracelet and eraser. The card said "lets have a 'do over' and can we be friends again" and the eraser said 'do over'(cute). So I guess they decided to end it and I'm happy they did - my daughter was more than happy to accept this gesture and reciprocated by giving the girl a card saying "I agree to a do over and being friends again". The older sibling isn't bothering my daughter either. I'm happy the girls have settled this and can now go back to interacting peacefully at school. I feel happy and glad it ended positively.
When this 1st happened I let the principal handle it and the girls were fine. Then the mom came to my door and I was kind and reassuring to her, but it went progressively downhill from there. I believe it would be long fogotten, if it was left up to the principal and the girls.