Best way to know is to look at her parents. If they are within breed standard, she most likely will be also. Ask the breeder what she thinks. By now there should be some pretty strong familial resemblance and you can tell which dogs your pup takes after in the pedigree. You can ask about healthy weight goals too. The nice thing about a breed standard like what we have for Goldens is that breeders who try to stay within it are rewarded with fairly consistent results with their puppies.
Here is the standard: Size, Proportion, Substance — Males 23-24 inches in height at withers; females 21 1/2-22 1/2 inches.
Length from breastbone to point of buttocks slightly greater than height at withers in ratio of 12:11. Weight for dogs 65-75 pounds; bitches 55-65 pounds.
Just remember that you want your puppy to grow slowly and he won't attain adult weight till well over a year old.
Here is the link to the page, you might enjoy reading up on the whole standard. AKC Breed Standard - Golden Retriever Club of America