Did you see her parents? That should give you an idea how big she will be.
If you dealt with a reputable breeder, she should know her lines pretty well and be able to tell you if her puppies grow quickly or slowly, when they stop growing, etc. Some puppies stop growing at nine or ten months, some continue to grow into their second year.
If you use the general guidelines, she would end up being 8-10 pounds, but that guideline seems to be wrong more than it's right.