At the time of the press release, Hawkins was charged with two felony counts of abandoning or endangering a child.
Miriam Davis said she remembers the girls well.
Hawkins told hospital staff that she and her children had been at Flat Rock Lake and the children were smelling flowers when they collapsed.
Amanda Hawkins was arrested in San Antonio on Thursday and is being held on $70,000 bond, Kerr County Sheriff Rusty Hierholzer said. The children were left in the auto overnight, until around noon on June 7.
The investigation started after Hawkins took the girls to a medical center in Kerrville, who were then taken in grave condition to University Hospital in San Antonio, Hierholzer said.
According to the Kerr County Sheriffs office, 19-year-old Amanda Hawkins knowingly left both her children, 1-year-old Brynn Hawkins and 2-year-old Addyson Overgard-Eddy, in a auto parked in front of a Kerrville home late Tuesday.
A joint investigation between the Kerrville Police Department, Texas Rangers, Child Protective Services and the Kerr County Sheriff's Office began on June 8, Hierholzer said.
The sheriff's office suspects that Hawkins intentionally left the girls in a vehicle while she was in a home from Tuesday evening until about noon on Wednesday near Kerrville. "She would like to go get you things and bring 'em to you", Davis said.
She attempted to bathe them but didn't immediately take them to the hospital because she "did not want to get into trouble", according to the news release.
"Right around 5 o'clock yesterday evening, they had to take both kids off the ventilator and both kids died", Hierholzer said.
"This is by far the most horrific case of child endangerment that I have seen in the 37 years that I have been in law enforcement".
Davis has known the children's mother, Amanda Hawkins, since middle school.
Charges against her might be upgraded after the case goes to a grand jury, the sheriff told KABB, and the 16-year-old male may face charges.