I'm Speaking to You!
Barking is as natural for dogs as speaking is for humans. They bark to alert us to intruders, or to tell someone to go away. They may bark when they are excited, or bored, or conflicted, or anxious, or out of frustration, or because they want something. It's a primary means of communication.
Even so, it's not always something that fits well into our life-style, especially for apartment block dwellers! Our job is to teach our dogs when they can legally bark (at the first sign of an intruder, perhaps) and when they need to stop (after the first initial flurry). We can do this by giving our dog something else to do, such as fetching a toy, while simultaneously imposing a time-out if she continues.
We also need to discriminate between watchdog and fearful barking. A dog that is vocalizing at squirrels or the postman is typically not upset. If she is barking because she is fearful, that is a whole different ball of wax. We would treat it differently. Talk to us about how we can help.