How to help my new boxer feel at home.?

My husband and I recently adopted a 2 year old female boxer named Shelby. We already have a male. She and the male growl at each other constantly, they fight over food, and if you show one affection but not the other at the same time they fight . Shelby, (to me anyway) acts like she is sad. She dosen't want to sit with us on the couch. She dosen't want to lay with me in the bed. She just acts like she is out of place. Is this normal? We have had her for 5 days and I had hoped she would come around by now. If you have ever had a boxer, they are very energetic, attention and affection seeking dogs. And she just isn't. Will she come around and if so how long does it normally take? I have always had dogs from when they were pups and I have never adopted an adult dog before. Also, any suggestions on how to make the growling and bickering stop? Its very sad, I just want her to be happy!