Morgan Lane Arnold's bedroom at her mother's house was painted pink and lilac, with white unicorns prancing in a border that ran along the walls. Even at 14, her mother said, she still believed in unicorns.

The room has been repainted recently, the unicorns vanished under layers of pale blue and sea green, and Arnold, at 15, is now an adult in the eyes of the law. She is charged with first-degree murder and four other counts in the stabbing last year of her father, prominent Howard County businessman and blogger Dennis Lane.

Her lawyer wants her case moved to juvenile court, arguing that she is not a danger to society and could be helped by treatment. The prosecutor opposes the move, emphasizing the seriousness of the crime and the potential danger. A circuit judge will make the decision after a hearing.

Arnold's boyfriend and former Mount Hebron High schoolmate, Jason A. Bulmer, 20, could be sentenced to life in prison after pleading guilty last week to first-degree murder. Prosecutors say he stabbed Lane to death with a kitchen knife at his home in Ellicott City early on the morning of May 10, 2013.

Prosecutors say Bulmer told police that Arnold told him to kill her father because "she was sick of him."

The killing shook Howard County, where Lane was well known through his work in commercial real estate, his column in Business Monthly and his blog. Those close to him have mixed emotions about how Arnold's case should be handled.

Friend and fellow blogger Tom Coale of Columbia said he understands the anger toward Arnold, but mostly wonders what Lane would want now for his daughter. Others, he said, are more certain.

"There are family members and friends who would like to see both of these individuals spend the rest of their lives in prison," he said.

Arnold's case unfolds as a dispute about Maryland's system of charging juveniles as adults for certain crimes moves to the General Assembly, which is considering a bill that would allow more teens who have been charged as adults to request transfer to the juvenile system.

The proposal is opposed by prosecutors, who told a state task force last year that the juvenile system is not equipped to safely hold violent youth defendants before they are tried and that the prison terms it allows are not long enough.

Advocates for juveniles say the current system does not curb crime, exposes youngsters to the violence and destructive influence of adult criminals, and ignores scientific evidence that adolescents are different from adults in their thinking.

Cindi Arnold says her daughter belongs in juvenile court. When arrested in May, her daughter was emotionally immature for 14, had been diagnosed with an anxiety disorder and Asperger's, a form of autism, and retreated from the difficulties of social life into fantasy, Cindi Arnold said.

"She literally still believed in unicorns and fairies and vampires," Cindi Arnold said. "For her, these were real things."

The girl is accused of plotting with Bulmer to kill her father and his fiancee, Denise Geiger, at the home in Ellicott City where Arnold lived when not with her mother in Catonsville.

Geiger was present during the attack that occurred about 4 a.m. in an upstairs hallway, but was not hurt. Lane, 58, was stabbed several times. He was found dead in his bed.

Assistant State's Attorney Danielle M. Duclaux told the court last week that the two teenagers exchanged Skype messages about killing Lane, making detailed plans in the days before the crime. Arnold egged Bulmer on, Duclaux said, and hours before the attack told him that she had unlocked the basement door so he could get into the house quietly.

Cindi Arnold questions how her daughter can be held to the same standard of responsibility as an adult.

"You're talking about a juvenile who does not yet have the physical capability of good judgment to see the consequences of action," she said. Cindi Arnold shared custody of the girl with Lane, to whom she was never married.

Attorney Joseph Murtha, who is representing Arnold, has filed a motion to have the case transferred to juvenile court. He told the court the case meets the legal requirements for transfer, saying Arnold does not pose a threat to society, that she would be a good candidate for treatment in the juvenile system, that she's never been transferred between adult and juvenile court before and that her mental and chronological age match.

In a motion opposing a transfer, prosecutor Douglas L. Nelsen emphasized the seriousness of the charges and the "risk to public safety." Nelsen declined to comment for this article.