The tenderloin is pretty sketchy, especially at night.
The area around Market and 6th st is where the drug dealers hang out.
Dolores park at night is a great place to get mugged, during the day it's fine as long as you keep an eye on your stuff.
Anywhere near Hunter's Point is sketchy, but there's nothing to do down there so she likely wouldn't be over there anyway.
The area bordered by Gough and Webster, and Turk and Fulton is where the low-income housing projects are. I'd avoid that area at night. There's also a little branch off of that rectangle which extends up Webster to Hayes that I wouldn't want to be walking in at night.
Overall it's a pretty safe city as long as you have your wits about you. Neighborhoods like the Haight, Inner Sunset, the Richmond, the Marina, Nob Hill, Russian Hill, Cole Valley, the Castro, NOPA, and Noe Valley are safe places. Downtown and SOMA are just slightly less safe. The Mission is slightly less so than those.