The teen, Molly Conley, a freshman student at Blanchet High School in Seattle, was out walking with friends around 11:30 p.m. when the shooting happened.
Conley and her friends were celebrating her 15th birthday which was Friday at a home of the father of one of her friends in Lake Stevens, said Father Jim Johnson, the priest at her family's church, Our Lady of Fatima.
Lake Stevens Police were called to the shooting at South Lake Stevens Road and 20th Street S.E..about 11:30 p.m., said Lt. Rodney Rochon of the Snohomish County Sheriff's Office.
Police have not identified any suspects, and no arrests have been made.
Conley, a 4.0 student active in sports and drama, was supposed to have a birthday party in Seattle on Sunday.
Her best friends who she was with on Saturday night were all from the tight-knit Magnolia neighborhood where she lived, Johnson said.
"Her mom wanted her known as someone who had a huge heart, a very loving person," Johnson said.
She has an older brother at Blanchet and an older sister who already graduated from the north Seattle high school.
Johnson said her parents' Catholic faith means a great deal to them.
"We really invite prayers for her parents and for the people who were with her there," he said.
Family gathered Sunday evening at Our Lady of Fatima Parish in Magnolia to remember Conley, and counselors, ministry staff and faculty will be available on Monday to talk with students at Bishop Blanchet, school officials said.
Meanwhile, Snohomish County's major crimes unit is assisting Lake Stevens Police in the investigation.
Detectives are trying to determine if other drive-by shootings that were reported in Snohomish County on Saturday may be connected to the shooting that killed Conley.