There is a wide range of normal sizes for infants, babies, even for toddlers. Your PD should plot your baby's growth on a chart and compare it with the average. Even if your baby's weight falls at the top or bottom of the charts, chances are she is still healthy and normal.
By 4 months, 30 ounces a day should take care of all your baby's nutritional requirements.
Babies give cues during feeding that indicate how hungry they are. Paying attention to these cues will help you determine when your baby has had enough to eat.
1)A hungry baby will latch on to the breast or bottle and suck continuously.
2)A baby who is getting full during a feeding will take longer pauses between sucking.
3)A full baby will turn away from the breast or bottle and not want to suck.
So just relax, your baby will be fine, If you have any concern about her gaining weight too slowly, talk to the PD.