The verdict was handed down Friday morning at the Longueuil courthouse.
She was sentenced to life in prison, with a possibility of parole after 10 years.
During the trial, Dennett testified about how she was taking care of the elderly woman, who was in a wheelchair, when she pushed her down the stairs and stabbed her multiple times.
The defence argued that Dennett was bullied by the victim.
Police were first alerted to victim's disappearance by a friend, who said she had not heard from Livingstone in days.
After receiving the call, police went to the victim's house and found her body on the floor of the furnace room, covered with a blanket.
A few days later, police tracked down Dennett to the Nelligan Hotel in Old Montreal, where she had booked a room using Livingstone's credit card.
Dennett said she was picked on by victim
Livingstone and Dennett, who were distant relatives, began living together in Brossard in May 2011.
The accused became a caregiver for Livingstone, who used a wheelchair and depended on the help of others for transportation and access to basic needs such as groceries.
But Dennett said tensions soon developed. In an emotional testimony, she explained how Livingstone continually picked on her and said nothing she ever did was right.
One day, Dennett said she couldn't take it anymore.
She described pushing Livingstone down the stairs and then stabbing her with a knife in the rib cage.
When the knife broke, Dennett said she went back upstairs to the kitchen to get another knife, which she used to stab Livingstone again, closer to the heart.