A 21-year-old New Hampshire woman who was critically injured in a Fourth of July car accident on Barnes Road died on Saturday, a spokesman from Brigham and Woman’s Hospital in Boston has confirmed.

Heather Laflamme of Berlin, N.H., was one of three people flown by medical helicopter to Boston hospitals after the car she was riding in, a red 2012 Jeep Wrangler, collided with a black 2009 Volkswagen Tiguan driven by a 19-year-old Cambridge man near the entrance to the Airport Mobil station. The accident took place just after 2 p.m. Wednesday. There were four occupants in the Jeep, all New Hampshire residents.

Ms. Laflamme, of Berlin, N.H., was ejected from the Jeep’s back seat, state police said.

Seth Jones, 26, of Dummer, N.H., a back seat passenger in the Jeep, was flown to Boston and admitted to Beth Israel Hospital with serious injuries. Margaret Jones, 51, of Dummer, N.H., a front seat passenger, was also flown to Boston and admitted to Beth Israel with serious injuries. Mr. Jones was reported in critical condition on Monday, while Mrs. Jones was reported in good condition.

The driver of the Jeep, Thomas C. Jones, 51, of Dummer. N.H., was transported to the Martha’s Vineyard Hospital with serious injuries, state police said. The driver of the Tiguan, Benjamin T. Johnson, was released after being taken to the Vineyard hospital for evaluation.

According to state police, the Jeep, traveling southbound on Barnes Road, apparently pulled to the right side of the road and then turned to the left to make a U-turn. The Volkswagen, which was traveling behind the Jeep, came up on the left side of the Jeep, broad siding it during the U-turn, state police said. The collision caused the Jeep to roll over and the Tiguan to veer off the road.

An investigation is continuing into the accident. The state police collision analysis and reconstruction team traveled to the Island on Wednesday. Investigators are interviewing witnesses and examining evidence, state police said.