The attack happened very quickly, and one bite was enough to inflict fatal injuries, she says.
The penguin was taken to a bird rehabilitation specialist but had to be euthanised due to the severity of its injuries.
While she praised the dog's owner for picking up the bird and contacting DOC, Ms Spencer says for the penguin, it was too little, too late.
"People don't like to think that their dog would attack wildlife, but it is natural behaviour for dogs.''
Christchurch City Council Animal Control Team Leader Mark Vincent says it is up to owners to control their dogs on beaches where wildlife is present.
In April, Ms Spencer picked up a yellow-eyed penguin from Southshore beach with dog-bite injuries after being alerted by a member of the public. It died later.
Little blue penguins, which are known as white-flippered penguins in Canterbury, nest in small numbers on rocky foreshores in the region.
At this time of year the penguins cross beaches almost daily and are pairing up and laying eggs. At only about 25cm tall and weighing just 1kg, they are unable to defend themselves from attack.
Members of the public are urged to contact the Department of Conservation via the DOC emergency hotline number 0800 DOCHOT (0800 36 24 68) to report injured native wildlife or instances of animal attack.