Caroline Goss, the Mattituck woman accused of killing a Hampton Bays boy while driving drunk last summer, now faces six months in jail after pleading guilty in April to vehicular manslaughter—and the victim’s mother said she is outraged and disappointed by the sentence.

The jail term that awaits Ms. Goss after her sentencing on Thursday, June 17, is the result of a plea bargain struck with prosecutors. Prosecutors said that they might not have been able to secure a felony conviction if the case went to trial, because evidence shows that the victim, 15-year-old Joseph Marino, swerved into Ponquogue Avenue on his bicycle immediately before he was struck by Ms. Goss’s vehicle.

“Given the witness statements and the accident reconstruction in this case, a conviction after a trial would have been problematic,” Robert Clifford, a spokesman for Suffolk County District Attorney Thomas Spota, wrote in an e-mail last week. “The plea and sentence of six months and five years’ probation assured the defendant was convicted of a felony, served some time in jail, and will be subject to multiple drug and alcohol conditions of a lengthy probation.”

Police said Ms. Goss, who was 34 at the time of the accident, was drunk when she struck Joseph while he was riding his bicycle on Ponquogue Avenue on the evening of August 12, 2009. Joseph was transported by helicopter to Stony Brook University Medical Center, where he died the next day.

Ms. Goss’s 6-year-old son was in the front seat of her car at the time of the accident, authorities said.

In Suffolk County Court in Riverhead on April 20, Ms. Goss pleaded guilty to second-degree vehicular manslaughter, a felony, as well as DWI and endangering the welfare of a child, both misdemeanors, and driving with an open container of alcohol, a violation, according to Mr. Clifford.

Ms. Goss’s attorney, Anthony Palumbo of Mattituck, declined to comment this week.

As a result of the plea bargain, Ms. Goss faces six months in jail and five years’ probation, Mr. Clifford explained. She is scheduled to be sentenced later this month before Judge Gary Weber. If Ms. Goss violates the terms of her probation, she faces up to seven years in prison, according to Mr. Clifford.

Joseph’s mother, Dorothy Marino, said this week that the sentence falls short of what she had hoped for.

“It’s just that I’m outraged at the entire legal system and how it seems as though the criminals have more rights than the victims, and that the victims just don’t seem to get the justice that they deserve,” Ms. Marino said.

“My son did not deserve what happened to him,” she added later. “He did not go out there expecting anything to happen to him. He went out there to enjoy the bicycle that he just got the week before.”

Ms. Marino and her husband, Phil, will file a civil suit against Ms. Goss within the next two weeks, seeking compensatory and punitive damages for the wrongful death of their son, according to Edmond Chakmakian, the attorney representing the family in the suit and a longtime friend of the Marinos.

“The proposed sentence is of little consolation to them,” Mr. Chakmakian said. “They feel that she should have paid a higher price­—more jail time. And they’re sorely disappointed in the way the criminal justice system worked in this particular case.”

Mr. Clifford said that if the case went to trial, prosecutors may have had a difficult time winning a felony vehicular manslaughter conviction because Suffolk County investigators determined that Joseph may have darted in front of Ms. Goss’s 2001 Jeep Cherokee before he was hit. “The evidence shows the victim swerved into the lane of traffic on Ponquogue Avenue and was immediately struck by the defendant’s vehicle,” Mr. Clifford wrote.

At about 8:40 p.m. on August 12, 2009, Joseph was riding his bicycle from Argonne Road East to Ponquogue Avenue alongside a 16-year-old friend who was on foot, Mr. Clifford wrote. At some point, the two boys encountered a girl they knew. Joseph was struck just as the 16-year-old boy was waving to the 15-year-old girl, neither of whom was identified, according to witness statements provided by prosecutors.

“I think Joey may [have] swayed into the road, and he got hit,” the 16-year-old boy said in a statement to police.

The 15-year-old girl told police that she was walking along the shoulder of Ponquogue Avenue, against traffic. As she neared Argonne Road East, the two boys passed her and waved, she told police. When the 16-year-old witness moved so she could get by, Joseph rode “into the roadway a little,” according to her statement to police.

“That’s when Joey got hit by a black SUV type of truck,” the 15-year-old witness told police.

When asked if her son may have swerved into the road, Ms. Marino said: “Unfortunately, there are only two people who are going to confirm that, and one of them isn’t talking and the other one can’t talk,” referring to Ms. Goss and the victim.