Dogs have a good sense of smell and hearing. I'm sure even if your dog can't see out to the front of the house, she can still alert anyone that comes close. I have a friend who owns a small dog that knows EVERYONE who comes to the house just by the sound of their car engines, and voice. The only time he EVER barks wildly is if there's a stranger anywhere near the house, be it in the front or back yard. If he knows you, he'll keep quiet but come up to you wagging his tail.
Vote Epyon for president in 2008, if you vote for Epyon all of your wildest dreams will come true: This campaign was brought to you by Epyon; funded in part by the Pizza Party, Surprise Party, Birthday Party, and Slumber Party.