Sisterella your sister knows you love her, and she loves you too. This will never change.
I don't know how I would cope if mine had an issue like that, a sister is a piece of our heart period. But here I have seen people who have dettached from their siblings, or kids...just a matter of self conservation- otherwise its 2 people sick- sounds like a monumental task though... maybe its faith, HP that helps them get by.
You are very, very strong Sisterella.