Sounds like typical pack behavior when a nervous new, hyper-excited and anxious dog comes into a new environment and has to try to establish some credentials. Try to let them work it out and step in and stop any really bad behavior such as biting but dogs use their teeth, loud growls and body language and play-fights/attacks as play but also to size each other up and occasionally do some light fighting at first. Remember that the new dog is likely scared and worried about the huge change in her life and just trying to stake out her claim.
If the animosity continues with biting/fighting after a few days, perhaps placing the new girl in the crate in the room with some toys, Kong with treats in it and a chewie so she can feel safe and secure as she settles into her surroundings for a period of time will help them adjust more slowly. As you play with your present dog near the crate to desensitize the new girl to this activity, toss the new girl a treat there in the crate so she will come to like the whole process and not be jealous. You might even rotate the new girl out and about for a time and put your older dog in the crate as you play with the new girl and toss her treats as this process begins to desensitize her. After a while, leash the new girl and allow her out but keep her back a bit as you play with your old dog, tossing treats to the new girl as you interact with old dog. When she acts accepting and friendly, you can allow the two to play for a very short period of time and then separate them.
In the meantime, read all that you can on the internet on pack behavior and interaction in dogs and you'll be very, very glad you learned all that you could. It will explain a lot about their behavior and help you understand the pack dynamic that will be taking place as they adjust to one another.
__________________  Jeanie and Tibbe One must do the best one can. You may get some marks for a very imperfect answer: you will certainly get none for leaving the question alone. C. S. Lewis |