A New Jersey school bus monitor has been charged with manslaughter and child endangerment after authorities say she was using her cellphone and failed to notice a disabled 6-year-old being suffocated by a seat belt.

Amanda Davila, 27, of New Brunswick, was charged in the death of Faja Williams, who was found unresponsive when she arrived at Claremont Elementary School in Franklin Park on Monday. She was taken to a hospital but was pronounced dead shortly after.

Davila was sitting near the front of the bus when it hit bumps on the road in Franklin Township, authorities said. The bumpy ride caused Williams to slump in her wheelchair, and the 4-point harness that secured her to her chair tightened around her neck, restricting her airway, according to the Somerset County Prosecutor's Office.

Davila was charged Wednesday and made her initial court appearance Thursday. It wasn't clear Friday if she's retained an attorney, according to the prosecutor's office.

Williams was born with Emanuel syndrome, a rare chromosome disorder that left her unable to speak or walk but still able to make sounds. She was attending classes as part of an extended school year.

"She was the sweetest kid you'll ever meet. She had the sweetest little laugh, little dimples and she just endured so much in her six years," said her mother, Namjah Nash. "She did not deserve this, to be taken away from us in such a way, that had nothing to do with her condition."

Nash told CBS New York that her daughter is nonverbal but is able to make sounds.

"Is it that loud on the vehicle? Is it that loud?" Nash said. "She makes sounds. She has a voice."

Faja's mother told CBS New York she got the call Monday, 45 minutes after her daughter was picked up from their home.

Authorities said Davila violated policies and procedures by using ear buds and her cell phone while she was supposed to be monitoring the child.

"This lady is on the cellphone. [Faja]'s back there fighting for her life. She's not even looking back," Faja's dad, Wali Williams, told CBS New York.

Franklin Township school officials declined to comment, citing the ongoing investigation.

Montauk Transit LLC, which operated the bus, told CBS News they were "devastated."

"We all extend our deepest condolences to the family and are grieving as a Company," Montauk Transit LLC said in a statement Friday. "All of our employees know that the safety of children we transport is our top priority, which is why we are fully engaged in the law enforcement investigation and support any punishment that the justice system determines appropriate for the bus monitor who has been arrested."

In:
• New Jersey
• School Bus
• Manslaughter