Hi Clare-
Most of what you are seeing is due to a few things. One is being a puppy, 2 is being an Aussie puppy which is a working breed designed to herd and 3 is lack of exercise.
None of these things require treats to work out, so you can eliminate them. Biting can be trained out of the dog by saying “Ow!!” when she bites you or is mouthy. No treats needed for that. Eating carpet can be fixed by replacing carpet (right when you see her going after it) with approperiate chew toys like Kongs and also by increasing exercise. A tired dog is a good dog. Barking may also be taken care of with more exercise. Also if you are not already, I would be kennel training her so that when you leave the house she can safely be in a kennel and there is no risk of her going after the carpet when you’re not around.
At 12 weeks they are just now beginning to understand what you expect from them. It may take a little longer to getting her potty habits under control, but once she is not getting so many treats that will help a lot. As far as growth goes, she can only grow so much for her breed, but she can become overweight which is the main problem. Google the Purina Body Condition Score and use that as a guide to keep track of her weight and make sure she is not getting heavy.
Treats should be given for really really important training like stay, recall, sit, down, leave it, not jumping. Things that you really want to reinforce, because they are important for good behavior and safety (recalling to you for example can save her life if shes running toward the road).
