Waiting until at least 6 months is really the best course of action. Their tummies at an earlier age just aren't ready to handle anything else besides your breastmilk. She is getting everything she needs from you right now. Many babies even go longer than 6 months before any kinds of solids are introduced.
It sounds like she's really not ready for the solids, what with the tummy issues and all. Rice cereal doesn't even have anything nutritional that baby requires. It's truly just a "filler" and to get them used to eating. You could just as easily start off with some fruits or veggies. Applesauce is a great starter.
There is some really good information here that I suggest you look over: http://kellymom.com/nutrition/solids/solids-when.html . Definately look at "Developmental Signs that Baby is Ready for Solids".
Here is some additional information: http://kellymom.com/nutrition/solids/delay-solids.html
Best of luck to you :)