Tane spent days in hospital and while he is doing well physically, he has permanent scars and has gone from being "Mr Independent" to an often scared, upset and withdrawn little boy.
Four days after Tane was discharged, Ms Donald went to the council with medical records and photos and made it "very clear" she wanted to press charges.
Last week she got an email from an animal management inspector saying the council had withdrawn the charges against the dog owner.
"Sadly the case will not be going to court. Sorry for any inconvenience," the email said.
Ms Donald was furious no one would be held accountable for what happened.
"I don't understand. I think it's just a copout. She gets away without even a slap on the wrist," she said.
Bylaws and animal management team leader Wayne Knightbridge said yesterday that Ms Donald had not reported the incident - rather, a dog owner did when she handed the dog over voluntarily to be put down for reasons she claimed were unrelated to the attack.
He said the reason Ms Donald was not kept informed about the case was simply because she "was not the complainant".
The owner was charged and pleaded not guilty in the district court. She denied it was her dog that had attacked Tane, claiming there were two in the hatchback at the time.
"There were no witnesses to the incident. Once the dog owner denied her dog was responsible it became incumbent on council to prove that her dog had attacked the child," Mr Knightbridge said.
"Council had no evidence to support the case that the defendant's dog was responsible ... either dog could have been responsible. On 9 June the council was forced to withdraw the matter ... because there was not direct evidence to support the charges."
Ms Donald was angry at the way the case had been handled and "absolutely bewildered" by the council's response.
"Why is the council letting such a serious matter slide? Because of their lack of communication and common decency my son was not given a fair shot at justice.
"The dog paid for what it did and was destroyed. And yet the owner, who raised the dog, has walked away without any repercussions at all."