It’s understandable but truly not helpful. We are all hard wired for survival - sometimes that wiring gets bashed along the way but it’s a protective mechanism that stops us dwelling on how risky life really can be. All sorts of things could derail us - it’s a miracle they often don’t. Our survival didn’t reduce someone else’s chance. If you believe in an omnipotent god or fate, you may find the reason why there. Or, like me, you may simply accept there is no complicated reason, it’s just chance again. You were fortunate, in time, in responding to treatment, your friend unfortunately wasn’t. Would she want you to feel guilt? Feel sadness, feel determination to remember her, but please don’t feel guilt. It’s corrosive and it does not belong with you. Best wishes.