M.B.
Don't do it. Her body is not ready for solids. I just read an article on line about this. No solids until 6 months, and no water or juice. She may look like she is ready or interested, but,I would wait. I have a 4 year old and a 4 month old and tried rice cereal on my first baby and all it did was constipate her. I stopped, and gave it to her again at 6 months. I wouldn't even think of feeding my 4 month old cereal now....way to young. Also, instead of rice, I gave my daughter infant oatmeal.
Good luck and congrat's!