I just got a 9wk old pommerian chi mix. wats the biggest she will get?

Most chihuahuas stay 2-6 lb. That is the standard, but I have seen them much bigger, over 12 lb. Pomeranians are usually just a little bigger than chis. If you saw the parents, the pup will likely stay close to their size, but there are exceptions. Sounds like the breeder was not a reputable one and she may not be telling the truth about what the dog may be mixed with. If the puppy got sick, you would have a hard time getting anything from the breeder. It would cost you more to sue her than you would be able to recover. Please take her to the vet to be checked and start shots if they haven't been started already. Also she will probably need to be wormed. Housebreaking should start immediately, but you should keep her from any public areas until she has had 3 rounds of shots. Normally you start training them around 6 mo.