At 4 months, I just set a time that I wouldn't feed him before (2:30) after he had done it on his own numerous times. Then I pushed that time further and further back the older he got, and when we got to around a 5am NF we just went cold turkey with it. He was a little over 6months at the time of the cold turkey.
I remember you posting a while back that she was consuming around 40oz of formula. Is she still taking as much formula as she was prior to you starting her on solids?