Sullivan, a San Francisco resident, was struck by a cement truck at 9:37 a.m. Saturday near Third and King streets, police said.
Both she and the truck were traveling west on King Street when they collided, according to police.
Sullivan was taken to a hospital where she died later that morning, police said.
The truck driver stopped immediately after the crash and is cooperating with investigators. Police are still looking into how the crash happened but do not think alcohol or drugs played a role.
The accident happened while large crowds waited to enter the 20th annual Giants Fan Fest event at AT&T Park.