Help For Friend? Dog Barking...

A girl I work with is having a hard time with her lab. She is thinking of rehoming it, but I think she would be willing to solve the problem if possible. She already has an older lab male, that she got as a puppy, that was her "dream dog". She got the female as a 10 month old, I believe. I'm not sure how old she is now..definately under 2yrs.

Anyways, the dog is doing pretty good except I guess with a huge barking issue. She says that especially if the dog is in the crate, and someone knocks on the door...or she sees or hears someone walk by the house...or if she sees even a shadow move that she's not sure of, she will go into a huge barking fit. She has small children...a four or five year old, and twins that are probably 2 years old, and it's getting hard when she puts them to sleep, at night and for their naps. Her and her husband have friends stop by randomly a lot, so I suppose it's beoming a big problem. She also seems to go into random barking fits for now reason, just out of the blue, and won't stop for 5-10 minutes. I suggested several things, and she's already tried throwing a can of pennies, ignoring, etc. and the dog dosen't seem to get better. I asked about excercise, and she said that she probably dosen't get enough, as her yard isn't completely fenced and the dog has to be walked on a leash. She admits that she works, goes to school full time, and has the kids and husband, and thus the reason for maybe rehoming. She is thinking about trying a bark collar...we were talking about pros and cons of them, and she will probably get a training collar where she can use the handheld remote at her discretion. Although I did mention that it might be a band aid for an underlying problem.

Any other suggestions would be wonderful.