Aaww, what a pretty girl! She could easily pass for a pure bred Lab. At 4 1/2 months my Caleb was 30.5 pounds (yep, I have his records right in front of me. LOL) . He's matured to 65 pounds (at the minimum weight wise for a male). And about 22 inches tall. In general, at 6 months, they're close to adult size, but aren't done growing yet. By a year old, you'll have a better idea of how tall she'll be (she could still grow some in height after her first birthday). She'll start filling out during her second year. Keep in mind, tho, that those are general statements- some lines aren't done filling out until they're 3! And, like Jackie said- Labs aren't supposed to be huge. Below is the part of the AKC breed standard regarding size.
Size, Proportion and Substance
Size--The height at the withers for a dog is 22½ to 24½ inches; for a bitch is 21½ to 23½ inches. Any variance greater than ½ inch above or below these heights is a disqualification. Approximate weight of dogs and bitches in working condition: dogs 65 to 80 pounds; bitches 55 to 70 pounds.