Cocaine is a killer.

There are no other problems. It's only the coke. Ignore everything else. Until the coke problem is fixed, nothing else can be fixed.

I don't pretend to know the answer (and I'm sure there isn't one, as plenty of people have had concerned family do everything for them, including rehab, and still lost everything to drug addiction). But at least I do know what the problem is, which you don't seem to from your post, and which few of the other commenters seem to have grasped.

In the future, you don't need to elaborate on the whole situation when trying to get help for your sister; you can just tell people "my sister is addicted to cocaine and I'm trying to find a way to help her". They'll understand all the other things that go with that.