One of the major advantages that dogs gave us when they first were evolving beside us was alerting us to things they could sense but we could not. Therefor, alerting us by barking is something that's natural, ingrained and difficult to maneuver around sometimes, because it literally is an instinct! Once a dog taps in on an instinct and gets rewarded by it (her environment responding to her instinct in a major way, positive or negative) it's tough to break.
Teaching "Quiet" helps a lot, and desensitizing her to the "coming and going" ritual could help, too. Every now and again during training sessions with my kids I'll go to the front door and ring the doorbell or go to the other side and knock. The quietest dog gets a treat, and I work with the one who's the loudest (my cocker spaniel) until I can knock or ring the bell and there's minimal noise. That way, when someone randomly comes to call, it's not such a disruption to their normal lives and when I ask them to calm down and be quiet it's easier for them to understand.
I also DO NOT open the door if we have a visitor unless my dogs are calm and quiet. My husband thinks it's rude to the person on the other side (LOL) but, hey, it's my house, my rules. They can wait a second or two so when they come in my dogs aren't all amped up and acting rude (sometimes my husband will just go open the door when the dogs are alerting and I can't stand it!)