A surveillance video shows 26-year-old Allison Matthews of Gaston County spending at least 30 minutes inside the store shopping while her daughters slept inside a parked car.
A woman in the parking lot heard the girls crying called 911.
Jennifer Shannon said she was frightened for the children.
"The child heard me say the doors are locked, and she immediately pulled up the lock and just jumped into my arms," Shannon explained.
Shannon kept the girls, ages 4 and 2, inside her car with the air conditioning on until police and paramedics arrived.
Police say Matthews went inside the store Saturday and left the children sleeping with the windows cracked on a 94 degree day. She told police she didn't want to wake them.
Police say paramedics made sure the girls were okay before releasing them to their father. Matthews is charged with misdemeanor child abuse.