The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at
Raising Your Dog with the Monks of New Skete For more on being top dog, see
Establishing and Keeping Alpha Position, Letting your dog know you are the boss
The above are fundamental techniques I suggest for almost all behavior problems and should help with barking too. The truth is, Labs usually don't bark that much and I don't have methods of controlling barking that I have been successful using. It isn't even in the manual for them. The manual does have a suggested reading list which I put in the sticky at the top of the dog forum. One I have read is The Other End of the Leash by Patrica McConnell.
She suggests the first step is not to yell at the dog. After all, usually if one dog starts to bark, any others around will to. So yell at your dog when it barks and it is happy to have you bark with it. Quietly tell it enough and walk over to it with a treat, doesn't need to be very big. Let him know you have it and use it to lure him away from what he is barking at if anything, and praise him as he shifts his attention to the treat and away from barking. Once away from where he was barking, give him the treat.
Unlike much of my other advice, this is not something I have tried and found works. It does come from a reliable source and I would trust it more than something I found on a website I know little about. I just hope she isn't smart enough to figure out if she barks, she gets a treat plus your attention.