A 17-year-old girl who was originally charged as an adult with abusing an autistic teenager has pleaded responsible to two misdemeanor charges in juvenile court.The teen pleaded "responsible" to second-degree assault and distribution of an obscene video on Thursday. Officials said it's the equivalent of a guilty plea in adult court.The teen is expected to be sentenced next week to a juvenile detention center stay that will last until her 21st birthday.Prosecutors said she and a 15-year-old girl recorded the sexual abuse and torture of a 16-year-old autistic boy they knew on their cellphones in St. Mary's County. The abuse reportedly took place between December and February.Shortly after their arrest, police said the girls acknowledged they made the recordings of incidents showing the victim being assaulted with a knife on multiple occasions, being forced to perform various sex acts, being kicked in the groin and being dragged around by his hair.A judge sentenced the 15-year-old in the case to six years in a juvenile detention center for her role in the assault, calling her a danger to the community.The 17-year-old could have faced up to 80 years in prison if the adult charges hadn't been lowered to juvenile court.