First off sorry to hear that fellow coli bruh
Support your friend and be their for her. Focus on things in life that you can control. Focus on the fact that God will only put you in situations he know you can get through. Tell her stories about people that have fought cancer and gone on to do great things. Make her laugh, shed tears of joy not sorrow. Now is the time where you can prove that being genuine isn't a lost art. Remember people are measured by intervals of distance traveled.
I had a friend die from cancer she was only 25. Also my mother currently has lung cancer. She completed chemo and is now onto radiation.