Alexis Simpson, the 19-year-old Bowie State University student accused of fatally stabbing her roommate last week, “got mad and reacted,” a Prince George’s County prosecutor said in court Monday.

Simpson, of District Heights, is charged with first-degree murder, second-degree murder and first-degree assault in the Sept. 15 slaying of Dominique Frazier, 18. The two women shared a suite on campus.

Photo gallery: Bowie State campus reacts to fatal stabbing in dorm

Michael Worthy, Simpson’s defense attorney, said in court that the stabbing was a “tragic accident.” He said Simpson tried to help Frazier after she was injured, and called 911.

“This is an isolated aberration,” Worthy said. “She is not the type of person who would hurt anyone.”

But Worthy also said his client was trying to defend herself. “There were individuals who wanted to do her wrong, or watch while wrong was done to her,” Worthy said. He did not elaborate.

During the Monday court hearing, Prince George’s District Judge Patrick Duley ordered Simpson held without bond. A preliminary hearing is scheduled for Oct. 14.

According to court papers, Simpson and Frazier began to argue Thursday night after Simpson turned off music that had been playing on an iPod in the suite they shared with two other students.

The argument escalated into a physical fight, court papers said. After Simpson was pushed into her bedroom by someone else in the suite, she emerged with what appeared to be a knife and stabbed Frazier in the neck, the papers say.

Christine Murphy, an assistant state’s attorney for Prince George’s County, said it was “no tragic accident.”

“This is her making a choice — a choice to end someone else’s life,” Murphy said.

Murphy said in court that two days before the stabbing, Simpson had posted a Twitter message that said: “I should have stabbed his ass.”

The women had known each other just weeks. Simpson, school officials said, had been randomly assigned to the four-bedroom suite after she transferred to the school from Clark Atlanta University. Witnesses told police the two didn’t get along and had been arguing in the week before the incident, court papers said.