Hi Lookup: Glad you found SR but also sorry you had to find SR. But you have found a place full of ESH (experience, strength, hope).
You have made some good moves to protect yourself. I think it is wise to hold someone at their word. Your sister's brain is like that of an undisciplined 3-year-old, and undisciplined 3-year-olds say all kinds of crazy stuff. But she is also an adult who can act on her words.
Keep coming back here. There will be others coming along shortly to respond to your post. But also I highly encourage you to find Alanon or Naranon meetings in your area because your sister's addiction has fragmented your family of origin big-time, and there really can be healing from that. You are full of all kinds of negative emotions right now (as anyone would be in your situation), and Naranon/Alanon is a good place to be able to get those feelings out so they do not stay inside your head banging around and causing you all kinds of damage.
Again, welcome to SR !