In sentencing, Justice Williams said the blackmail had a major impact on the victim.
"It's a relatively significant amount, not a small amount. The threats of violence from very dangerous people obviously caused [the victim] to be petrified. Another factor is that you kept returning for more."
Todd had admitted the violence offences, the majority of which occurred in 2011, when she attacked the blackmail victim on several occasions. She broke his arm with a skateboard, threw a steak knife at his head, sliced his cheek, stabbed him in the leg and threw a ceramic bowl at him.
Judge Williams lamented the impact her drug use had on her child, described as an "innocent and vulnerable victim" of her habit.
Traces of the drug were found in a sample of the child's hair. It was likely to have come from breathing in smoke or putting something tainted in its mouth, the judge said.
He urged Todd to quit drugs.
"You and your children are repeating the mistakes that you blame the last generation for ... Therapy and treatment are what you need. All I can do is plead to the corrections service to provide this help for you."