I think you are going to rapidly get a ton of responses advising you against getting two puppies at once, particularly from the same litter....the main reason being is that they will tend to bond to each other and not necessarily to you. Plus also for the reasons you mention double the cost of everything, in addition to you needing to know that you have the time/energy to train, play, socialize them separately.
Plus given what you have mentioned about the one that your purchased being 'purebred no papers' tells me all I need to know about the ethics of your breeder (or rather should I say the lack of ethics
). I would wager that neither of the parents were health tested, titled and likely should never have been bred in the first place.....even though they may have 'looked good'. I'm no expert but I certainly can't tell whether a dog is dysplastic or not based upon what it looks like in most cases (unless it is a severe case of dyplasia). There are pups that are bred by COE breeders from fully health tested parents which develop dysplasia.....how do you know that your girl who comes from unknown history may not come down with dysplasia or a heart problem......and what if you compound that by having two littermates with the same problem. You can quickly look at tripling your vet bills when dealing with that type of scenario.
Personally given that you have already purchased the one girl..... I would train her, love her, spay her at an appropriate age, enjoy her to pieces, find a venue that you can both enjoy, research the breed and then in the future, research what is and what is not a good breeder and contact a COE breeder in the future when looking for your next pup.
Heather Peters