my DD was not as little as your DD, but did drop from just above the 50th to below the 25th centile , she was snacker, from birth. small amounts of milk ,little and often, when she was 10 months old she refused all solids for 10 days after an illness.
i had to change my expectations of her and stop comparing her to her brother who would eat from morning till night...!
i did BLW after i got tired of seeing my lovely organic homeade purees refused, and she enjoyed being more in control of her intake. it took until she was 2 years old to actually ask for food and say she was hungry
if she is busy playing or colouring, she won;t eat
i give 6 small meals a day, and she will sit and eat with us, but not eat much.
she is not a fan of water or juice. also, i know if she does not eat much, she has a good pint of milk or so a day.
she is developmentally fine, always has been , slow to talk, but is catching up. happy, healthy , alert , no digestive problems.
HV told be to stop bringing her for weighing so often as it was upsetting me! HV totally fine about it.
for there to be an average, 50th centile, some babies need to be above it, some below it.
my friends DD was same size as my DD at birth, but rapidly hit the 90th centile, very chunky baby, exclusively BF for 6 months, but really a big baby. we both used to sit and bemoan our babies, one skinnymalinks , one chunky !!
they have pretty much evened out, although DD is more delicate, she finally got a pot belly on her ,and does not have that awful hollow belly when she lies down now
anyway , enough rambling....
DD is not a big eater, i doubt she ever will be, there is more to a child's health than their weight gain...
DD will eat anything, but just tiny amounts
hope that helps a bit !