A drink-driver who crashed her car into a house in the Perth suburb of Merriwa, killing a baby, has been sentenced to more than three-and-a-half years in jail.

Melissa Waters, a mother of three, had a blood alcohol level of 0.17 when she lost control of her car and smashed into Nate Dunbar's bedroom in January.

The eight-month-old baby was crushed and his death was witnessed by his seven-year-old brother who was also trapped in his bedroom.

The District Court was told Waters had been drinking with friends and drove despite them telling her not to and attempting to hide her car keys.

Waters pleaded guilty to a charge of dangerous driving occasioning death.

She was sentenced to three-years-and-eight-months' jail and will be eligible for parole after serving 22 months.

Nate Dunbar's mother Stacy says she hopes her son's death stops others from drink driving.

The car smashed into Nate Dunbar's bedroom. ( Supplied )

"I never want anyone to feel what we feel," she said.

"Our lives were shattered that morning when the car drove into our boy's bedroom while Nate was asleep in his cot," she said.

"We could only hope that the sentence given to her would put a small dent in her life. It is nothing compared to what was done to our lives.

"Drinking and driving is a choice. A very arrogant and selfish choice.

"No-one forces you to put your keys in the ignition after drinking and the reasons people choose to drink and drive are always selfish.

"There is no adult in Australia that doesn't know the potential consequences. There is never a reason to justify drink driving.

Melissa Waters lost control of her car. ( ABC News: Oliver Peterson )

"I think the hardest part of standing here today is knowing that I will not be the last mother standing here pleading for people to stop drinking and driving.

"That means that someone sitting on the couch watching me make this speech is going to be here knowing the pain and hurt that I feel everyday, all because somebody else sitting on the couch right now hasn't listened to a word I've said and it breaks my heart."

In a statement released at a previous court appearance Waters said apologising was not enough for what she had done and she wished she could change places with the baby.

She said she would spend the rest of her life attempting to atone for the pain she has caused.