An Arlington County mother of three was struck by a dump truck and killed near Nottingham Elementary School on Monday as she tended to one of her young children in the back seat of her van, authorities said.

Police said Jennifer Lawson, 39, had just placed the child in a car seat when the dump truck headed west on North Little Falls Road struck her and the van. The force of the crash tore off the van’s door, but the child in the car seat was not injured, said Lt. Michael Watson, a county police spokesman.

Lawson was taken to a hospital, where she died, police said.

The 11:30 a.m. crash occurred in the 5900 block of North Little Falls, across the street from Nottingham, where at least one of Lawson’s other children attends school, Watson said.

John Schmidt, a friend and former co-worker of Lawson’s at the Schmidt Public Affairs firm, said those who knew the caring wife and mother were struggling to process the news.

“This is all very raw right now,” Schmidt said during a brief telephone interview. “My heart is just truly broken.”

Schmidt said Lawson was a “loving, doting and devoted mother” who “had this very special close relationship with her husband.” Schmidt said Lawson had joined him when he left another firm to set out on his own.

Mary Zehe, president of the Nottingham PTA, said Lawson was an active member of the group who volunteered to decorate the school’s front hallways.

“She was very friendly and outgoing,” Zehe said. “In general, we have a very strong community and always pull together when anything like this happens.”

The driver of the privately owned truck stayed at the scene of the crash and was cooperating with investigators, Watson said. He was not injured, Watson said.

Watson said that although the mechanics of the crash were relatively straightforward, investigators were looking into some of the finer points — including precisely where Lawson was standing and how fast the truck was going. He said investigators also are planning to perform a full commercial-vehicle inspection of the truck.

“From an accident point of view, it was a very simple accident, but it gets complicated when you start trying to figure out speeds and where they were on the roadway,” Watson said.

Watson said police had not determined who was at fault or charged anyone in connection with the crash.

Schmidt said Lawson worked at his firm for about five years but had left the company. He said he recalled her bringing her children to the office for lunch.

“It doesn’t make sense,” he said of her death. “We just lost a really, really special person.”

Michael Alison Chandler contributed to this report.