I would just let her eat when she wants too..
Adriana use to be that way.. She NEVER ate the "required" amount.. I did bottle feed and all she would eat during her first few months was maybe 1 - 1 1/2 oz's a meal and at that time she was drinking breast milk (I exculsively pumped). I was unable to breast feed because she was a lazy eater and would fall asleep at the breast. Even when she was 10 months old, the max she would drink was 3-4 oz's of formula when kids her age should be drinking 6-8 oz's a meal.. I never forced her.. She did gain weight slowly, but she never dropped in percentiles until she was 15 months old.. But her head, weight, and height measurements always stayed in the same percentiles, she was growing evenly and she still grows this way today..
I know it's hard not to worry.. Because I did when I was in your shoes..