The judge ruled that Carter, now 20, can remain free on bail but ordered her not to make any contact with Roy's family, and she can't leave the state. She faces a sentence of probation to 20 years in prison.
The sensational trial in Taunton offered a window into teen depression and suicide through text messages and Facebook communications.
Carter was 17 when she sent Roy dozens of messages urging him to take his own life in July 2014. Roy, 18, was found dead of carbon monoxide poisoning in his truck in a store parking lot in Fairhaven, MA.
"I thought you wanted to do this. The time is right and you're ready, you just need to do it!" Carter wrote in one message.
Prosecutors said that in addition to bombarding Roy with text messages, Carter also gave Roy advice when he got out of the truck as he was inhaling the gas and told her he was scared. "Get back in," she told him, according to a friend who testified Carter described the conversation in a text message to her about a month after Roy died.
Carter's lawyer, Joseph Cataldo, argued Roy had a history of depression and suicide attempts and was determined to end his own life. He said Carter initially tried to talk Roy out of it and urged him to get professional help, but eventually went along with his plan.
An involuntary manslaughter charge can be brought in Massachusetts when someone causes the death of another person when engaging in reckless or wanton conduct that creates a high degree of likelihood of substantial harm.
Dr. Peter Breggin, a psychiatrist testifying for the defence, said Carter was a "very troubled youngster" who suffered from depression. At the time of Roy's death, Carter was taking Celexa, an antidepressant Breggin said targets the brain's frontal lobe, which controls empathy and decision-making.
Breggin said Carter was in the grips of a "grandiose" delusion that she alone could help Roy find his way to heaven and she would care for his family.
Prosecutors focused on a series of text messages Carter sent Roy in the days before he died by suicide.
"You can't think about it. You just have to do it. You said you were gonna do it. Like I don't get why you aren't," Carter wrote to Roy the day of his death.
Prosecutors argued the text messages support their claim that Carter caused Roy's death by recklessly helping him poison himself.
Carter and Roy met in Florida in 2012 while visiting relatives. Their relationship largely consisted of text messages and emails.
If you are thinking about suicide, please call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255) or the Suicide Crisis Line at 1-800-784-2433.