Was the breeder aware that you wanted a dog that would grow to < 7 lbs as an adult? Did she tell you that your dog unlikely to be > 7 lbs?
Basically, if you feel that you were explicitly misled, I would call the breeder or write her a letter to express your disappointment. I think it's always better to complain (does that say something about my personality?

) because maybe this person will think twice before pulling a fast one next time.
I can understand that you may feel a bit of "buyers remorse" because these puppies are so expensive. It's a big purchase, and commitment. However, I think everyone is right that you will end up adoring her even if she ends up weighing TWENTY pounds.