Sharfeddin was born Heather Mason in remote Rosebud County, Montana to a forester father and an artist mother. In 1968, the Mason family moved to Riggins, Idaho on the Salmon River and later to nearby Lucile, where they lived in the remodeled Cow Creek pioneer schoolhouse. In those early years Sharfeddin and her two sisters enjoyed the remote Idaho back-country, collecting Indian artifacts and roughing it with local ranch kids. Sharfeddin remembers visiting such legendary places on the Salmon River as the Shepp Ranch and the Polly Bemis home, which were inaccessible by automobile.

In 1977 Lynn Mason moved the family to East Lansing, Michigan where he obtained his masters degree in forestry at Michigan State University. They were happy to return west to Missoula, Montana in 1979. Sharfeddin attended Hellgate Junior High and Big Sky High School, graduating in 1984. She moved to Portland, Oregon in 1986 and still lives in the Willamette Valley.

Her first novel Blackbelly, published in 2005 by Bridge Works Publishing, is set in central Idaho where she grew up. She draws her imagery and characters from those early years and the folklore of the Salmon River.

In 2006 her second novel Mineral Spirits was published, also by Bridge Works Publishing, and is set in remote Mineral County, Montana. Sharfeddin has called her work "contemporary western", which she defines as stories about the rural west that take place during the twentieth and twenty-first centuries. She promotes this genre through talks and seminars.

In 2009 her third novel Windless Summer was published by Random House (Delta imprint), and is set in the Columbia River Gorge in the fictional town of Rocket, Washington.