Court heard the woman, who was 17 at the time of the crash in 2010, was speeding and texting.
She had also been drinking.
The woman, now 22, pleaded guilty in youth court to criminal negligence causing death and criminal negligence causing bodily harm.
A judge refused a Crown request to sentence her as an adult.
Following her custody term, she will also be under mandatory community supervision for one year.
The Crown had asked that she serve five years in prison as an adult. The defence requested a youth sentence of one year in custody.
The woman cried as she was led out of the court in handcuffs and family and friends of the victims hugged each other in the hallway.
"I feel like we were not given justice for these two girls that passed away and of course the three others that survived with the psychological effect and the physical effect of this," said Anita Subramaniam.
Her younger sister, 17-year-old Amutha Subramaniam, died in the crash along with Senhit Mehari, 19.
Lysbeth Arthur survived, but suffered brain damage and had to learn to walk and talk again. She said outside court that what she has gone through should be taken into account in court.
"Even just emotional, psychological injury is not something that we should look at as less than death. Because those things stay with you."
The Crown had alleged the driver planned to drink and drive that night, based on a text message exchange with a friend. After attending two parties, her friends tried to take her keys away but were unsuccessful.
Evidence showed she was texting and going 20 km/h over the speed limit while on cruise control, when her car collided with the victims' vehicle at an south side intersection. Her blood alcohol level was .07.
Psychologists said the woman is being treated for post-traumatic stress disorder and attention deficit hyperactivity disorder. They said she has expressed remorse and is a low risk to reoffend.