E.T.
As long as she is gaining weight you don't need to worry about how much she is eating. When our daughter was 4 months she was only eating 3 to 4 oz bottles. Sometimes she would only eat 2 oz at a time. Both of my nieces had been taking 6-7 oz bottles when they were that age. I started to panic but when I asked our doctor about it he said we didn't need to worry as long as she was gaining weight. Now at 7 months she is finally starting to take between 6-9 oz at a time.