Dear R.,
My children are 42 and 39 years old now, so this idea comes from the old school for feeding babies. When babies were not satisfied with just formula, they were started on rice cereal. I think it may have been a tablespoonful of cereal mixed with enough formula to make it runny once a day to start. We also gave them steralized water between feedings. Back then, formula was placed in glass bottles, steralized and refrigerated. So when you steralized your formula bottles, you also steralized the water in bottles too to keep on hand for those times when just a little hydration was needed. I don't believe bottled water from the grocery store is steralized; you may want to check that out before you use that as a shortcut.
It could be that this might help you to start increasing the time between feedings. Try to increase the time between feedings by 10-15 minutes to start. If your little girl doesn't get fussy, wait until she does. Don't just automatically feed her because it's been 2 hours and 15 minutes.
Any questions about initiating the rice cereal should be discussed with your doctor if it will make you more comfortable. I can't imagine that he/she will object. Good luck!! Have your camera ready; this makes for good pictures.
Sincerely, M.