Describe a selfish friend

Nina and I recently stopped talking with each other. It started from Nina first. She suddenly turned cold to me and I don't know what the reasons are. In the class, she sat at another seat, she no longer talked with me. I tried to keep being friendly but she still acted as if we were not friends. Finally I stopped talking as well. I basically don't like her for a long time because she is very selfish ,and she think everybody else is selfish like her. one time, when we worked together to write a report, we had agreed that I would do the first part and she would do the second part. However I was so busy with my classes and don't understand how to answer the questions so I have her come to my teacher's office to ask. Nina thought I was not responsible for my job and let her do the hard part.