Hi Sigmagrrl! Wow! Travelling alone in a big city takes guts girl!
GiantsChic is right about Great America- unfortunately, it's closed now and won't reopen until March. When will you be here?
You should check out Golden Gate Park. There are TONS of things to do there! You can go to the Aquarium, Japanese Tea Garden, botanical gardens, or rent a boat at Stow Lake.
As for food, San Farncisco is known for their diverse and amazing restaurants! You can find something great practically anywhere you go! I will happy to suggest something more specific if you want when you decide which neighborhoods you are most interested in.
If you want to take a short drive, Monterey is a cute little seaside town about an hour and a half south of SF. It's famous for their aquarium and shops. There is also a HUGE shopping center on the way in Gilroy full of outlets.
I work for the Automobile Association, so I give out maps and touring advice everyday. You can PM me if you want. I would be happy to help!
In the meantime, here are three websites that are really cool:
www.sfvisitor.org
www.citysearch7.com
www.sfstation.com
SF is so awesome and I'm so glad you're checking it out!