You should actually be starting out with 1/4 TSP of rice cereal per 1 ounce of milk. You can offer it 1-2 times per day to start, but be wary of her bowel movements stiffening up drastically. The consistency should be very thin, and as she gets better learning how to make the chewing motions and swallowing properly, you can gradually thicken it. I'm a bit surprised that you're BF'ing her and starting her on cereal so soon... it's very often recommended that nursing babies don't start solids until they're 6-8 months old at the youngest. Since your siggy said that she's extremely fussy, keep in mind that this young, the cereal may actually make her more fussy, especially since you're giving her too much cereal per milk in your TB per ounce of milk ratio (which is a choking hazard, as well as nearly impossible to digest).
EDITED: Since the OP has a thin skin, my sources come from a pediatrician who is on the AAP board as well as extensive research of my own. My 2 cents wasn't appreciated by the OP but it IS correct. The directions on the box are for babies that are older than 4 months. It's also a fact that many nursing coaches will advise nursing mothers to hold off on solids until the baby is at least 6-8 months old. That's also an advisement of the AAP.
Obviously I'm not stupid, and whatever you end up feeding your baby and when is up to you... but to discount someone's heartfelt advice that they're offering out of the kindness of their heart and their 3X plus experience and child education is rude.