I think they just look solid so my mind saw "bigger." I have one of the Wimaumau rescue giants (44 pounds), but even my 2 previous gals were far from petite... about 26 to 28 pounds. My dream of a petite 18 pound basenji just never happened, lol.
What a sweet face! Thank you for taking her in, she needs a forever home.
As Pat indicated, unless you have info on the parents being clear, or at least one clear, she should be tested for Fanconi asap.