my 9 month old does the same thing. she thinks it is so funny! at home, i start screaming with her and she stops right away because even though she thinks SHE is funny, for some reason, i guess she just thinks it's weird when i do it! in public, i usually have some goldfish or cheerios on hand and when she starts getting loud, i shove snacks in her mouth. she likes to eat, so it distracts her from screaming....

my older two used to be screamers too. we couldn't ever get my oldest to shut up, but she stopped eventually after a couple of months.... i think she'd learned a new annoying trick by then! can't remember about my middle child....

anyway, you're not alone! until you can get a handle on it, don't worry about it. i think that most people understand that babies scream. just make eye contact with the people around you, smile and shrug in that "what can i do???" kind of way.... those people will look and see how adorable your baby girl is and then they won't mind her screaming so much! i promise, it works! :)