SAN ANTONIO, Texas -- A 19-year-old woman from Texas was arrested after authorities say she left her two young daughters in a vehicle for 15 hours, resulting in their deaths.The Kerr County Sheriff's Office said Amanda Kristine Hawkins took 2-year-old Addyson Overgard-Eddy and 1-year-old Brynn Hawkins to the hospital Wednesday.According to police, Amanda arrived at Peterson Regional Medical Center with the victims, claiming they had collapsed while running around and smelling flowers at Flat Rock Lake and may have gotten into something poisonous.Investigators said they later determined that the children were intentionally left in their mother's car overnight, until about noon on June 7, while Hawkins and a 16-year-old male friend were inside another friend's home.Kerr County Sheriff Rusty Hierholzer said that at some point, the 16-year-old went out to the car and slept for a while but then went back inside the house. KABB reports that Hierholzer said he also understood someone inside the house could even hear the children crying and told her to bring them inside the house but she didn't. The children were without food, water or restroom visits during their 15 hours in the car, according to the Sheriff.The sheriff stated after returning to the car and finding the children in trouble, Hawkins did not immediately take the children to a hospital. He said she instead tried to cover up the incident by bathing and redressing the children. Hierholzer said it was his understanding the children were unconscious at this point.Sheriff Hierholzer said Hawkins finally sought medical care after being talked into it. After arriving at the hospital in Kerrville, the children were taken to University Hospital. Hierholzer said sometime around 5 p.m. Thursday, both girls were taken off ventilator systems and passed away.The sheriff said their records showed "no history" with Hawkins but that investigators determined it was not the first time she had left the children in a car.Hawkins was charged with two counts of child endangerment, but Hierholzer said the charges could be upgraded after the findings of the case are presented to a grand jury.She was taken to the Bexar County Jail following her arrest and will remain there until her transfer back to Kerr County. Her bond was set at $35,000 for each charge.Hierholzer said the 16-year-old who was with Hawkins may also face charges.