Abduction could've occurred after she left the bridge? What streets occur as you get off the bridge? Is it a residential area? Sorry, I know nothing about San Fran.
When you walk across the bridge, there is a parking lot for GGB on the Marin side and then it's about 3/4 mile downhill on the side of a road/highway (with no sidewalk) to Sausalito which is upscale residential and a touristy seaside village. It's a common ride for bikers but less friendly for walkers. You can, however, loop left through a tunnel to Cronkite Beach where there is also a youth hostel. Would be nice to think Syd went there and hooked up with some other travelers. Wonder if they have checked there.