EVERETT — A Snohomish girl will be locked up for 13 years after pleading guilty Wednesday to a brutal attack on two schoolmates in October.

Lawyers had expected to argue Wednesday whether the girl, who turns 16 next month, should be charged as an adult. Instead, the attorneys reached a plea agreement that should send the teen to a juvenile lock-up for five years. Then, after her 21st birthday she’s expected to serve out the remainder of her sentence in adult prison.

The agreement is a compromise that gets the girl the mental-health treatment her lawyers say she desperately needs. It also keeps her locked up longer than if she’d been convicted solely as a juvenile. The teen’s sentence is about mid-range for an adult conviction for first-degree assault with a knife.

“We wanted the victims to be adults for quite some time before they have to worry about seeing her on the street. They deserve that,” Snohomish County Prosecuting Attorney Mark Roe said. “We also do recognize that the (defendant) is a child herself. We made a way so she can stay in the juvenile system to get some help. She is going to get out, and she is a part of the community.”

The girl pleaded guilty Wednesday afternoon to first-degree assault and second-degree assault for the Oct. 24 attack that nearly killed April Lutz and injured Bekah Staudacher, both 15.

April was stabbed more than a dozen times while inside a bathroom at Snohomish High School. Her friend Bekah was slashed in the arm and stabbed in the back trying to stop the attack. The girls were getting ready for class when they were ambushed.

Neither girl knew their attacker, an upperclassman.

April barely survived. She was stabbed in the heart and a lung. Doctors said that her recovery was a miracle.

The honor student returned to classes in January, but has since been struggling to catch up with her school work.

“She’s gone from an outgoing, happy-go-lucky girl to one that cries out in her sleep, and only feels safe when she is surrounded by those who love her,” her mother Sue Lutz told the judge Wednesday.

April in December told The Herald that she clearly remembered the attack. Fellow students and teachers found April crumpled on the floor in the bathroom, bleeding from multiple wounds.

Snohomish paramedics raced her to Providence Regional Medical Center Everett. There, doctors opened up her chest in the emergency room to control the bleeding that was putting pressure on April’s heart. She left the hospital less than a week later.

April and Bekah will have to live with the horrible images of that morning for the rest of their lives, said Seattle civil attorney Sim Osborn, who represents the families. The girls’ parents are relieved that the defendant will be locked up and unable to harm their children, he added.

“It is so difficult to balance justice and understanding in a case like this that involves a juvenile, but we feel the plea agreement that was struck is a fair one,” Osborn said.

The victims’ parents offered their gratitude to the community, calling the support nothing short of remarkable. John Turner, who was Snohomish Police chief at the time of the stabbing, was in the courtroom along with the detectives who investigated the case. The victims didn’t attend.

Sue Lutz wore a pink T-shirt that read: “Small Town. Big Heart.”

“We are most thankful for our daughter’s well-being and that she and April are both still around to help one another return to their normal lives as much as possible,” Mark and Christa Staudacher wrote in a prepared statement.

Sue Lutz told the judge that she wants to feel compassion for the defendant, but she also wants to protect her daughter and other children.

“The girl who attacked my child is obviously a sick, troubled individual. She’s slipped through the system once with some very obvious signs that she was a threat to those around here. We cannot let that happen again,” she said.

Defense attorney Caroline Mann advocated for the girl to receive the intensive therapy only available through the juvenile justice system. Her client had been spiraling downward in crisis. Her mother and school officials had taken appropriate actions, but the seriousness of the girl’s illness went unrecognized, she said.

“We like to think we can prevent these tragedies, but some things cannot be predicted,” Mann said.

She told Superior Court Judge Larry McKeeman that the girl’s family was in the courtroom, but decided not to speak publicly, instead relying on the letters they submitted to the court. The girl’s mother wept as her daughter pleaded guilty to the charges.

“The girl who caused such terrible damage is not the child they knew,” Mann said.

They are hopeful that with treatment she will return, the veteran public defender added.

The girl, wearing shackles, maintained her composure through the hearing. She politely declined to make a statement when the judge asked if she had anything to say.

The day of her arrest she told detectives she’d been thinking about stabbing someone for a couple of days. She packed two knives in her backpack before leaving for class. She waited in a bathroom stall for about four minutes before she repeatedly plunged a large kitchen knife into April, who was standing at a sink.

The defendant’s medical and school records show that she had told adults in 2011 that she was having thoughts about homicide and suicide. She had been seeing a therapist and receiving medication for depression since February 2011. Her mother had discovered that the girl had been cutting herself and noticed a drastic change in the girl’s personality, dress and school performance.

The girl told a school counselor in April that she was having thoughts of harming people. She was expelled from the school the following day after two friends reported that the teen had threatened to stab one of the girl’s boyfriends. School officials insisted that the girl get professional counseling before returning.

The girl attended out-patient services at Fairfax Hospital for about eight days and returned to school in May. The hospital concluded that she was safe to resume classes. She then had irregular visits with a therapist for the next eight months, court papers said. Her last visit was about three weeks before the assaults.

In explaining the stabbing, the girl said she didn’t plan to kill anyone, but felt the need to hurt somebody, court papers said.

Snohomish County deputy prosecutor Cindy Larsen and Mann worked together over weeks to craft the unique resolution, which finally came together late Tuesday. They recommended that the girl be convicted as a juvenile for the assault on Bekah. They asked that the defendant be held in juvenile detention until she is 21, a sentence well outside the standard range.

They also agreed that the teen would enter an adult guilty plea to the attack on April, an act that should keep her in adult prison from age 21 until she’s about 29. That conviction also means that she will be under the supervision of state Department of Corrections for three years once she’s released. That post-conviction monitoring wouldn’t have been an option if she’d been convicted only in juvenile court.

The resolution balances the need for rehabilitation best achieved in the juvenile justice system and also adds protection to society by keeping her locked up for longer, McKeeman said.

Roe, who attended the hearing, said one thing he was going to take away from the case was the way the community came together.

“My kids don’t go to Snohomish, and I don’t live there, but I will always be a Panther fan because of the way the kids, staff, aid car folks, and community rallied around these two victims and saved one girl’s life,” he said. “The violence that happened is any parent’s worst fear, but the way everyone swung into action was awesome.”

Diana Hefley: 425-339-3463; hefley@heraldnet.com.