Ashley Lucier was found Thursday morning in Genesee County's Mount Morris Township. Some passersby, believed to be students at Flushing High School, covered Lucier and called 911.
Lucier was hospitalized in critical condition on Friday.
Police said there were more than 50 vehicles in the area of the crime scene that were stopped by officers in hopes that someone saw something.
Township Police Chief Scott McKenna said, "This is somebody's daughter."
Police don't know how long Lucier was in the ditch.