I definitely don't think that you did anything wrong in this case. She was the one who had crossed the line and crossed over boundaries that she shouldn't have, and that isn't fair for you. You need your privacy and she needs to respect that, sicknesses or not. And by her constantly talking about being sick and her diseases and bad luck- it seems like she needs a therapist, not a friend. You were trying to be a friend, and it wasn't working. So just don't be so hard on yourself. Situations like this happen- she was investing so much into you emotionally and thats not fair.