She was abusing the other passengers and engaging in public obscenity. At the least, disturbing the peace and disorderly conduct.

Was the child in danger? What if she had chanced upon someone as aggressive and uncontrolled as herself, but more physical. Would she used the boy as a shield? It is more than reckless to pick a fight with strangers on a bus. I think that evoking "big brother" is over the top. I think at the least she needed to be interviewed by public safety professionals to try and determine how much risk she poses to the child and to herself.