Her office is at 870 Market Street. MapQuest placed this near the Powel St. Cable Car turn-around. To my surprise, this is the Flood Building! Built before the 1906 earthquake, the steel framed Flood Building is very 'Sam Spade' inside. It reminded me of older skyscrapers I'd seen in Chicago.
The ground floor was used by Woolworths until 1992. I shopped there once. It had a breakfast counter and it was very old fashioned. Now the ground floor has clothing stores, and is part of the Union Square retail area. If you're in the area (or just tired of waiting in line for a Cable Car) walk into the lobby and look at the exhibits. Then ride a lift to any floor (I was on the 9th floor).