M.B.
Honestly, I would hold off. If she's able to sleep that long of a clip at night then solids aren't needed yet. How's she growing? Is the doctor concerned about reflux? If she's keeping the formula down pretty good though and has a decent weight gain and a schedule you are happy with then there's no need to introduce solids just yet. Maybe if she starts to wake up earlier for her morning feeding you might want to start by giving her a little cereal at her evening before bed bottle. That's how I did it with all of my kids. Kept their bellies nice and full so they'd sleep better at night. No need to mess with what isn't broke right now and if she's growing and developing normally with no health concerns like reflux then hold off about a month and a half with the cereal.