I think the OP is saying that people were advising her to fly to the greater Los Angeles area (including Anaheim) from San Francisco rather than driving.
I'm a little confused about her plans and the logistics, also. I think maybe they have a round trip flight from Australia to Los Angeles and then were thinking of driving up to San Francisco, dropping the car and flying back to Anaheim (getting a car again?), going to Disneyland and then flying home.
Since the itinerary isn't clear maybe the best thing to do is give facts.
There are three main driving routes between San Francisco and the greater Los Angeles area. Highway 5, 101 or the coastal route through Big Sur.
Highway 5 can be done in a day. Google says it's a 6:14 drive, but realistically it's probably 8 hours with stop offs, lunch and possible traffic. Highway 5 is the fastest option and mostly goes through boring dessert scenery.
Highway 280/101 south through San Jose, Salinas, etc will take an hour or so longer than highway 5 but it's prettier.
Going along the coast through the Big Sur area has spectacular views from winding roads along seaside cliffs. If you go through here from northern to southern California it will take much, much longer and you will want to stop a lot for the amazing views. To be safe without too much driving in a day you will need to break the trip into two days. Many people break their trips into three days if they want to see many sights along the way. They may stay in someplace such as Monterey/Carmel or Santa Cruz north of Big Sur and another stop south such as in Cambria, San Luis Obispo or Santa Barbara.
Flights are quick between San Francisco and LA area, about an hour or less of flying time.
You'll need to decide what makes sense for your schedule and what you want to see and do with the time you have.
Edited: 1:30 pm, January 13, 2013