I agree, they should definitely be from a breeder! Pet store chins are usually chins that the breeders have considered as non breeding stock, which is why they are sold cheap to the pet stores, and the pet stores just jack up the prices and make them look like real great chins, or something they have that is "rare". when in reality, those chins could be prone to mals or heart murmurs or anything health related.
But at least you are looking into the pros and cons before doing it, and at least waiting til she is of age.
Do you have pics?? we always love pics!!