Dunn, a San Francisco resident, was walking west on 18th Street around 2:30 p.m. when she crossed Hartford Street and was struck a bus that was turning left on to Hartford Street from 18th.
The victim was about 90 percent of the way across the street when she was hit, causing fatal injuries, police said.
Paramedics pronounced her dead at the scene.
The bus that struck Dunn was a shuttle for the F-line, according to Muni officials. There is no regularly scheduled bus service on Hartford Street, but police said the street is a common route for F-line shuttles.
The driver remained at the scene and will be taking a chemical test, police said.
The Police Department's Major Traffic and Hit and Run divisions are investigating the accident.