BOSTON (AP) — A young Massachusetts woman who as a teenager sent her boyfriend text messages urging him to kill himself before he did so has asked the state's highest court to overturn her involuntary manslaughter conviction.

Michelle Carter's lawyers say in the Feb. 5 appeal to the Supreme Judicial Court that a conviction based on "words alone" violates her free speech and other constitutional rights.

The 21-year-old Carter was convicted in June in the 2014 death of 18-year-old Conrad Roy III and later was sentenced to 15 months in jail. Carter was 17 when Roy died.

A judge said Carter caused Roy's death when she told him to "get back in" his truck as it was filling with carbon monoxide in Fairhaven.

A prosecutor says the conviction was warranted.