Tell your friend to go see a doctor immediately. Force her. Tell her parents, your parents. Someone. Breast cancer is one of the worst cancers a person can get. Why? Because it can spread throughout your entire body if left unchecked. The breasts are riddles with lymphatic "veins" that travel throughout the entire body. When the cancer spreads to the lymphatic system, it's pretty much over. It's very hard to treat because cancer can appear anywhere in the body after it reaches the lymphatic system. Please so your friend a favor and get her some help.
You can get breast cancer at any age. Even men can get breast cancer.