Michelle Carter will be released from jail for good behaviour after serving a majority of her 15-month sentence, in a decision that sparked an angry reaction from the family of the man she urged to kill himself.

Carter, who was convicted of involuntary manslaughter for urging Conrad Roy III to kill himself in 2014, is getting out about three months early, with jail officials saying that state law mandates early release in cases of good behaviour. She will now serve five years of probation.

But the release, and its rationale, has been criticised by the victim’s family, who claim that the woman who urged the 18-year-old to take his life should not be walking free.

“The sheriff should serve the rest of her time. He lets her go because she’s a good girl? She’s not a good girl,” the grandfather and namesake of the dead boyfriend, Conrad Roy, told the Boston Herald.

Carter’s Massachusetts manslaughter conviction and case garnered national attention, and tested the boundaries for how much culpability a person can have for simply speaking.

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Her lawyers argued in a recent Supreme Court appeal that the conviction violated their client’s First Amendment rights and that “words alone” are not enough for someone to be held responsible for another person’s death. The court declined to hear the appeal last week.

During the original trial, the jury heard sordid details of the days leading up to Roy’s death, in which a then-17-year-old Carter repeatedly urged her 18-year-old boyfriend in texts to kill himself and chastised him for not going through on his plans.

Then, on the day of his death, Carter reportedly spoke with the victim after he became unsure about his plan to die in his parked truck, which he had rigged to fill up with deadly carbon monoxide. Following the phone call, Roy returned to the truck, and died.

The call in question wasn’t recorded, leaving prosecutors to rely on those earlier texts to prove her intent.

Carter, now 23, first went to jail last February, but had attempted to avoid jail time altogether following her 2017 conviction, with her lawyers initially arguing successfully for a stay in her case as they appealed the conviction. That stay was revoked when the state’s Supreme Judicial Court upheld the conviction.

In September, she was denied early release by the state parole board, with members of that panel saying Carter displayed a “lack of empathy” for “facilitating” Roy’s death, and said her release was “not compatible with the best interest of society”.

The death and conviction has inspired an HBO documentary, and legislative efforts aimed at cracking down on suicide coercion. The bill, known as “Conrad’s Law”, would make manipulating someone into killing themselves a crime punishable by jail time, with a five-year maximum sentence.