Gia Soriano, also 14, was targeted during a gun rampage by fellow pupil Jaylen Fryberg near Seattle on Friday.
Her family said in a statement they were “devastated by this senseless tragedy”.
Another girl was killed in the attack, at Marysville Pilchuck High School.
She has not yet been formally identified.
Three other students targeted by Fryberg – including two of his cousins – remain in hospital. Two are in a critical condition.
All were shot in the head after the boy pulled out a weapon and started firing in the school cafeteria.
Reports have emerged about the heroics of one teacher, Megan Silberberger, who ran to the scene of the shooting and “did everything possible to protect students”, according to a statement from her union.
It was unclear whether Fryberg had killed himself deliberately or whether the gun had been fired by accident as he struggled with the teacher.
Fryberg, who was from a prominent Tulalip Indian Reservation family, was described as a popular, outgoing student, though messages he posted online before the attack suggested he had been “broken” by an unspecified event.
One pupil at the school told the Reuters news agency that the attack was related to a “fight over a girl”.