How quickly you transition really depends on your dog's digestive system and how she's handling it. My only suggestion is to determine how many calories she needs and make sure you aren't over feeding. Foods like Orijen are very high calorie, probably more than the Purina you were feeding ( don't know that for sure... but it would be my guess). Many people way overestimate the amount of food a pupper needs and, believe me, it's much easier to keep them lean than to try to take off extra pounds. And the amounts suggested on the bags are ridiculously high in most cases.