I don't know if you have had any success, but I think Melissa had a point. By the age of about 5 months, a baby is learning to relate cause and effect. She cries, she gets picked up, so she cries to get picked up. I would dedicate one or two days to try to retrain her. Of course, you should discuss this with the parents before you try it, since she's not yours.
What I would do is when you get her in the morning, hold her for a few minutes. While you're holding her, explain (not in baby talk) that you're going to put her down, and you will pick her up in a little while, but only if she is not screaming. You see, it's a struggle of wills, and so far she has won. You have to win this time, and never let her win again, if you're going to have any peace. Stay near her (and yeah, if you need to, try the ear plugs), and let her cry it out. The worst thing she can do is cry all day, and that isn't likely. She'll probably fall asleep first. Sing, talk to her, show her toys, interact with her as much as you can, or play with the other children while she's watching. Don't leave her alone. I would suggest putting her in a playpen that you can move, or if you pick her up to move her (say to the highchair to feed her), just move her and put her down, don't cuddle in between.
When she quiets down, praise her and scoop her up and reward her with a 1/2 hour or whatever of being held and fun. Then put her down again and start over. If you win once, you will win quicker the second time, and even quicker the third time. Just remember, it's a battle of wills; to have peace, you must always win and she must never win. Soon she'll find she's happier yielding.
Hope this helps!