The 40-year-old woman was arrested after being spotted driving erratically in Looe in Cornwall at about 21:40 GMT on Monday, Devon and Cornwall Police said.
Officers said a seven-year-old was taken into emergency care because no other family members lived in the area.
The woman remains in custody.
She was due to be interviewed at a police station in Plymouth, officers said.
A mother was arrested on suspicion of drinking and driving with her daughter in the car, leading to the girl being placed in foster care.