A Montgomery County woman charged in a hit-and-run last summer pleaded guilty Tuesday to one count of an accident involving a serious injury.

Suzanne K. Lammers, 76, of Hepburn Drive in Villanova, faces a minimum 90 days in prison or under house arrest, attorneys said.

She pleaded guilty to one count of an accident involving death or personal injury - a third-degree felony - in critically injuring 13-year-old Andrew Mallee of Bryn Mawr last July. She also pleaded guilty to a summary offense of leaving the scene of an accident without stopping and rendering aid.

Andrew was airlifted to Children's Hospital of Philadelphia, where doctors treated him for head and leg injuries. The accident caused hearing loss in his left ear, and he is awaiting surgery this fall to restore his hearing.

Andrew was riding his bike at noon July 15, 2009, on Bryn Mawr Avenue near New Gulph Road, when he was struck by Lammers' gold 2002 Volvo station wagon, police said. Lammers continued west on New Gulph, turned into Bryn Mawr College, and then continued home, passing the scene of the accident. She parked the car in her garage and covered it with a blue blanket.

Two weeks later, investigators received an anonymous tip and found the vehicle with a large hole in the windshield.

At the time of her arrest, Lammers told officers she thought she had hit a deer. She said she became frightened when she heard police sirens and drove away instead of waiting at the scene.

In court Tuesday, Lammers heard the facts of the accident, gripping a handkerchief, before delivering her guilty plea to the judge. The third-degree felony carries a maximum of seven years in jail and a $15,000 fine.

"She did admit her guilt today," said Deputy District Attorney Thomas McGoldrick. "She didn't when she should have. In fact, she actively took steps to avoid being caught."

Lammers' attorney, Frank DeSimone, is requesting that she serve the minimum 90 days under house arrest, pending a presentencing investigation to determine whether her home is suitable.

"This is a 76-year-old lady who raised two children, who's lived a very nice life. She's not a criminal. She made a mistake," DeSimone said. "Jail is for people you need to protect society from; Ms. Lammers is not one of them."

But the prosecution wants Lammers to spend the 90 days in jail because of the severity of the injuries Andrew suffered and what McGoldrick called Lammers' "egregious" behavior after the accident.

Andrew's injuries included a broken leg and fractured bones in his head and left ear, which caused hearing loss.

A civil suit also has been filed against Lammers and is expected to move forward now that she has pleaded guilty, said Richard J. Hollawell, the family's attorney.

Lammers is still driving. Whether she continues to do so is "for the DMV and the state of Pennsylvania to decide," her attorney said. "It's up to them."

Lammers posted the necessary 10 percent of her $50,000 bail and awaits sentencing in 90 to 120 days.

Contact staff writer Julia Terruso at 610-313-8110 or jterruso@phillynews.com.