At the age of 17, Michela Howeth Harriman of Cambridge had already demonstrated an uncommon commitment to other people. When Miss Harriman, who would have entered her senior year at St. Mark’s School in Southborough in the fall, died in a car accident while visiting friends in Vermont on Sunday, she was a seasoned world traveler who was raising money for Tanzanian schools after seeing them on a family trip.

In 2003, the Harriman family traveled to Africa, visiting villages and schools. Miss Harriman was shocked to see the shack-like school buildings, particularly in Tanzania, and learn that some children didn’t have books, said her godmother, Donna Brescia. "Her heart was so big, and she just really had a conscience even as a 15-year-old," Brescia said.

"In her short life, this was a life-altering experience for her," added family friend Cheryl Kiser. When Miss Harriman heard that building a school cost only $3,800, she knew she could help. She and her sisters, twins Alexandra and Serena, 14, began raising money for the Friends of Tanzanian Schools.

The fund-raising effort was just the latest manifestation of a special personality that close friends say had always been evident.

"Her spirit came through in her smile and eyes she had such a big presence and energy," said Kiser, whose family often traveled with the Harrimans.

By age 9, Miss Harriman had proved herself a lifesaver: While on a trip to Italy, she jumped into a pool and saved a 2-year-old child who had fallen in, said Brescia.

She was also talented musically, performing a pitch-perfect "Amazing Grace" at age 3, said Brescia.

At St. Mark’s, she was going to be a prefect in the fall, was a serious tennis player, and was captain of the varsity squash and junior varsity soccer teams. She also acted in several plays at St. Mark’s.

"This was an incredible kid," said Brescia. "She was going to change the world. Maybe her legacy will."

Besides her sisters, Miss Harriman leaves her parents, Kristen Wainwright and Richard Harriman.