considering she'll be basically full grown by 9-12 months, doubling in size isn't uncommon for any dog at that age.
BEAUTIFUL pup, btw. ;f
my GSD is 72 lbs and a LOT bigger than my g/f's aussie lab mix, but lb. wise they are only 8 or 9 pounds difference. her aussie is a lot smaller, but solid as hell and thicker to boot.
pups will grow faster than you can handle and eat a LOT while they are growing. after that, its a totally different story...
just for a size comparison ;e
my pup is 72 lbs, g/f's is right around 63...but hers looks SO much smaller