I think a food diary including how much (and what) she drinks will give the paed a good head start anyway. If you or your DP are slight or were as kids then perhaps that is also worth noting also, if your parents have any info too that could help.
AB's can make your tummy pretty upset too so maybe that has not helped. Certainly if she seems to be eating lots and is happy and alert - minus the ear infections then surely that should make them happier??
One thing that may be relevant is not using low fat dairy etc - kind of the opposite to what most people do.
xx

ETA I have a friend whose 5yo has just hit 16kg and another whos 3yo twins were only 10kg at ~ 20months also so I think it is not unusual but worth following up ITMS