Puppy is terribly sick! Help! Fast!?

My sister just got this puppy 5 days ago. She got it from the pound, they found the puppy on the side of the street without her mom. So they adopted the pup and named her Sadie, but she's sick! Her stomach is bloated, she has a fever, and her nose is really dry! They say shes 8 weeks but she barely has any teeth?! She's a bet hound/lab mix. Whats wrong with her? How old do you think she really is??? HELP!