You shouldn't feel selfish about having emotions that are difficult to deal with - it's really hard, and sad, to have someone you care about be sick and suffering. They're real, valid feelings. You might try talking to a therapist; you might try talking to a friend and finding out that hey, they feel the same way. Staying positive and hopeful is great, but come down to it, a loved one sick and hurt plain sucks, and getting wound up in the idea that one needs to stay positive does more harm than good for a lot of people. It's not like feeling angry, or overwhelmed, or scared, cancels out your concern for your friend, nor does it cancel out how she feels about her situation. I'm sorry you and your friend are going through such a tough thing.