Judge denies delay in trial for woman who allegedly encouraged her boyfriend's suicide.

A woman who allegedly encouraged her boyfriend to take his own life has had a request to delay her manslaughter trial denied.

US woman Michelle Carter is accused of sending dozens of text messages to her 18-year-old boyfriend Conrad Roy III in July 2014 urging him to kill himself as he had planned.

The 20-year-old is set to stand trial on March 6 over Roy’s death, after a judge rejected a plea by her defence lawyer Joseph Cataldo to have the date pushed back to April or May, The Boston Herald reports.

"Oh, that’s not happening. That’s not happening," Taunton Juvenile Court Judge Lawrence Moniz said.

"We’re not going to put it out that far."

The defence lawyer said he wanted time to investigate possible factors in Roy's death, such as the anti-depressant drug both he and Carter were reportedly taking, as well as reports of domestic violence in Roy’s family.

"There’s a lot of documents involved. There’s a lot of experts involved. There’s a lot of witnesses involved. … I just don’t want to be rushed, and I don’t think it’s appropriate on a significant case like this," Mr Cataldo said outside court.

"I think it’s relevant, but it will be up to the judge to determine whether a jury should know about that."

The then 17-year-old Massachusetts girl had allegedly sent a series of texts to her boyfriend, with whom her relationship was largely online, between 6 July and 12 July 2014.

"I just want to make sure you’re being serious. Like I know you are, but I don’t know. You always say you’re gonna do it, but you never do. I just want to make sure tonight is the real thing," Ms Carter wrote in one text.

“(D) on’t be scared. You already made this decision and if you don’t do it tonight you’re gonna be thinking about it all the time and stuff all the rest of your life and be miserable.

"You’re finally going to be happy in heaven. No more pain. No more bad thoughts and worries. You’ll be free,” said another.

"Always smile, and yeah, you have to just do it. You have everything you need. There is no way you can fail. Tonight is the night. It’s now or never."

Carter convinced Roy that his parents would be able to "accept" his death.

"Everyone will be sad for a while but they will get over it and move on. They won’t be in depression. I won’t let that happen. They know how sad you are, and they know that you are doing this to be happy and I think they will understand and accept it," she wrote.

"Good because it’s time, babe. You know that. When you get back from the beach you’ve gotta do it. You’re ready. You’re determined. It’s the best time to do it."

After Roy’s death,  Ms Carter tweeted a message encouraging anyone feeling suicidal to get help.

If you are experiencing mental health issues or suicidal feelings contact Lifeline on 13 11 14 or Beyond Blue 1300 224 636