Not eating what she should

My baby girl is not a big eater. The internet says 2.5 oz a day per pound of weight. So since she’s 12.1 lb, she should be drinking 30.25 oz a day. However, we are lucky to get 25 oz I her a day. Anyone else not have a great eater? She’s gaining weight, but not at the rate she should. She fell off her original growth curve and is down to the 21st percentile from 54 at birth. The doctors aren’t too concerned, but I am. She lets us know when she’s done eating. There is no way to get more into her. Even if we wake her at night, she won’t eat.