J.V.
I have a very simple rule in this house: we do not speak whinese.
So, when she starts, just tell her "i'm sorry, we don't speak whinese. If you would kindly use your normal voice, I'd be happy to help you in any way I can."
I have another rule too, if you are going to pitch yourself on the floor or throw a tantrum, you can go to your room until you are calm. My 4 year old will go from a crying fit to a perfectly normal voice in 3 sec if I remind her she has to use a normal voice or she can go to her room..... This doesn't work as well with the 2 year old crowd, but I do send my 2 year old to his room sometimes and it works.