If you were to do the city bus route (as opposed to renting a car) what I would do is Metrolink. OCTA Route 43 (the one that stops at the Harbor Blvd entrance to DL) also goes to the Fullerton Metrolink station. From there you can catch a train to LA Union Station and I would think either a train or bus from there would get you to the beach. I've taken the OCTA busses several times and have never felt unsafe, though I'm a 300 pound male so I don't consider as much to be a threat as others.