It´s deffinately not a Dogo Argentino because they have very short hair as pups..they resemble dalmations (short coats,white,stocky etc).I know because there are ALOT of them here and it happens to be one of my faves

This/your pup has fuzzy hair,like a 2 week old husky would have.It´s paws are also very small,so I´m guessing its a medium/small size breed what ever it is.Is she a mix? How come your sister has puchased a dog yet doesnt know what she is? Disnt she see the parents or at least the mother?