A Potomac woman pulling out of her driveway Sunday night struck her 7-year-old daughter, leaving the child with critical injuries, Montgomery County police said. They said the mother thought the girl was inside the house.

Wenhua Song, 41, of the 9900 block of Potomac Manors Drive, left her house to go to the grocery store about 9:15 p.m., police said. Her two daughters — ages 7 and 16 — planned to stay home.

But police said they think the younger daughter may have decided at the last minute that she wanted to go with her mother. As Song left the driveway, police said, her 2007 Mercedes-Benz GL450 struck her daughter — 7-year-old Xitong Kong.

Around 9:36 p.m., police said, they received a call for an alarm in the same block. When officers responded to that home, they were told a man had observed a person “lying in the Song driveway” and called 911. The alarm call at the neighbor’s house was not related to the accident, police said.

Officers went to the Song house and found the child unresponsive, police said. They said Song had just returned home after realizing she forgot something.

Cpl. Rebecca Innocenti, a police spokeswoman, said Song told officers “she had no knowledge she had struck the child.”

“She came back from the store and that’s when she found her child in the driveway,” Innocenti said.

The young girl was taken to Inova Fairfax Hospital with life-threatening injuries and remains in critical condition.

Innocenti said there are no charges at this time in the case.

Jennifer Jenkins contributed to this report.