Texas mother jailed in deaths of 2 toddlers left in car 15 hours: police The local sheriff calls it "the most horrific case of child endangerment."

 -- A Texas mother is accused of intentionally leaving her two young daughters inside a car for more than 15 hours, leading to their deaths, authorities said.

Amanda Hawkins, 19, was arrested in San Antonio on Thursday and faces two counts of abandoning or endangering a child, according to the Kerr County Sheriff's Office. Bond has been set at $35,000 for each count. Hawkins is being held at the Bexar County Adult Detention Center in San Antonio while awaiting transfer to Kerr County, the sheriff's office said.

"This is by far the most horrific case of child endangerment that I have seen in the 37 years I have been in law enforcement," Kerr County Sheriff Rusty Hierholzer said in a statement Friday.

According to Hierholzer, Hawkins and a 16-year-old male friend showed up at Peterson Regional Medical Center in Kerrville on Wednesday with her two daughters, 1-year-old Brynn Hawkins and 2-year-old Addyson Overgard-Eddy. Hawkins allegedly told medical personnel her daughters had collapsed after visiting Flat Rock Lake where they smelled flowers. The toddlers were transferred to University Hospital in San Antonio in "grave condition," Hierholzer said.

A joint investigation by the Kerr County Sheriff's Office, the Kerrville Police Department, the Texas Rangers Division and Texas Child Protective Services later determined that the two little girls had actually been left in their mother's car overnight "intentionally," from Tuesday night until about noon Wednesday, while Hawkins and her friends were inside a residence, according to Hierholzer.

"Upon discovering the girls, the mother attempted to bathe them and did not immediately want to take the girls to the hospital because she didn't want to get into trouble," the sheriff said in his statement Friday.

Brynn and Addyson died at the hospital Thursday night, Hierholzer said. The investigation is ongoing, and autopsies were scheduled for Friday at the Bexar County Medical Examiner's Office.

With the death of the girls, Hierholzer said Hawkins could face upgraded charges after the case is presented to a grand jury.

Hierholzer said the case will be handled by district attorney Lucy Wilke, who did not immediately respond to ABC News' request for comment Saturday.