If the dog is barking when she's alone, it's much harder to correct. The key to working on any behavioral problem is to interrupt the behavior (either with words or a leash/collar, etc) and give the dog an alternative behavior. I agree that if you teach her to bark on command, that you can then teach her "Quiet." I'd also control her access to the areas where you know she's going to bark (i.e. looking out a window or door). Controlling the environment is a big part of controlling barking. I know this because I have Malinois and they are quick to bark at things in the environment. If she's barking when she's alone, sometimes the answer is a bark collar.
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