The Supreme Court on Monday left in place the conviction of a Massachusetts woman who sent her boyfriend text messages urging him to kill himself.

Michelle Carter is serving a 15-month sentence after being convicted of involuntary manslaughter in the 2014 death of her boyfriend, Conrad Roy III. A judge determined that Carter, who was 17, caused the death of the 18-year-old Roy when she ordered him in a phone call to get back in his carbon monoxide-filled truck that he’d parked in a Kmart parking lot.

The phone call wasn’t recorded, but the judge relied on a text Carter sent her friend in which she said she told Roy to get back in. In text messages sent in the days leading up to Roy’s death, Carter also encouraged Roy to follow through with his suicide plan and chastised him when he didn’t, Massachusetts courts found.

The case has garnered national attention and sparked legislative proposals in Massachusetts to criminalize suicide coercion.

Carter’s lawyers argued in their Supreme Court appeal that the conviction should be thrown out because it was an “unprecedented” violation of her free speech rights that raised crucial questions about whether “words alone” are enough to hold someone responsible for another person’s suicide.