7 weeks and aggressive with me and litter mate

Hello my name is Michelle and my girfriends pom had puppies and i am going to be taking one. I choose the puppy i wanted when she was 4 weeks old. She was very calm and cuddly and just an overall sweetheat. So I go and visit her every other day and as the time has past she is currently just over 7 weeks she has become quit aggressive with her litter mates and when i go grab her to stop the little fighting she get super growly and bears her teeth at me. I know alot about dogs and I own 3 already and i also own my own grooming salon. But i am wondering if this is just a stage she is going through and if you have any suggestions on how to stop this behaviour? Is this even normal. I was super excited on getting a new puppy but now im kinda nervous. Should I be? I just figure shes going to take more training but i dont want to go about the wrong way or make it worse. Should I deciplin her at this age. Im just confused and i dont know how to approach the situation.
Any suggestions are greatly appreciated

Thanks you so much for your time
Michelle