Anna, I'm so sorry about your friend. I've never really lost a close friend to illness, but my sister had a couple of friends that died in high school - 1 from cancer, 1 from suicide, both tragic.
Being a pediatric resident I also watch families suffer through their children's illnesses on a daily basis, but watching the pain from the outside is obviously a little different. I can only imagine the heartbreak that these families and friends are coping with. It really breaks your heart and makes you feel like the world doesn't make any sense at all.
I'm so sorry for what you, your friend and her family are going through.
Jill