A drugged driver who caused the death of a cyclist in a hit-and-run collision at Victor Harbor, south of Adelaide, has been sentenced to five years in jail.

Samantha Magdaleine Farrer, 40, was found guilty of an aggravated charge of causing death by dangerous driving and leaving an accident scene over the crash in December 2013.

Farrer had methylamphetamine in her system when she drove into mother-of-three Kathleen Heraghty, 48, who was cycling on a straight section of Inman Valley Road.

Judge Gordon Barrett has sentenced Farrer to five years' imprisonment, with a non-parole period of three years and two months.

He told her he did not find good reason to suspend the sentence, or release her on home detention.

The judge said that Farrer had had little or no sleep after attending a Christmas party and had told a passenger she had hit a sign or a fruit stall.

"Ms Heraghty's body was flung by the force of the collision against the left-hand windscreen ... it would have been obvious that you had collided with someone," Judge Barrett said.

"While I accept that you are sorry to the family of the deceased, you do not accept legal responsibility."

The fatal crash happened on a straight section of road in broad daylight. ( ABC News )

Defence had pleaded for leniency

During sentencing submissions, Farrer's lawyer argued she should be spared jail because her 15-month-old son would suffer separation hardship.

The court heard that in another case, a sentence had been reduced on the grounds that South Australia did not have facilities in prison for mothers and babies.

Judge Barrett said he acknowledged that Farrer's imprisonment would affect her young son.

"I accept that separation from you may have detrimental effects on him," he said.

Prosecutor Amelia Cairney had previously said the offending was too serious to warrant leniency, saying the incident was aggravated by the use of methylamphetamine prior to the collision and the decision to leave the scene.

She said others needed to be deterred from the type of dangerous driving that killed Ms Heraghty.

Judge Barrett also disqualified Farrer from driving for 10 years, starting from when she is released from prison.