I wouldn't discount the smaller gal too soon. She could be your most prolific layer and they have away of having growth spurts. She may never be as big as her mates but she could come very close in a few months.
I can second this! My two smallest NN pullets lay eggs like crazy, and their eggs are pretty big for their size too, ranging between 1.85 and 2.1 ounces consistently at 10 mos. of age. And one of those "little" pullets wound up filling out very nicely....she just did it more slowly than the other girls did while still laying 5-6 eggs per week.