You figured it out yourself. She is going through the puppy equivalent of the teenage stage and testing her boundaries.
Teenage puppy stage: The dog's character begins to form at this stage. The owner must impose their authority so the puppy dog knows who's the boss and hey should begin with the training. It is also time to start ridding them of bad habits, since once they are a year old it makes it much harder. Dog must be able to go out, relate to other dogs and people, and have plenty of exercise. They must follow a routine so they are well balanced.
At some time during this training stage the young dog may become stubborn and even appear to forget orders or habits it had learnt before. This is all part of its adolescence. The dog tests their master to see who the pack leader is. It is very important to enforce authority.
The dog begins to be independent around five and six months. It must learn how to walk on the leash, turn, stop and respond when they are loose and their owner calls them.
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