I had a family member go through something similar. ^This is good advice, al-anon helped my parents a lot. I'm not an expert- but based on my experience here's what I'll say. She may have had to give up her old life entirely in order to move on. The thing about addiction.. it changes you. It's hard because that's still your sister but she's not the same person you remember, and she will always be an addict from now on.

I'd recommend sending a Facebook request if that's what you want but I would let her be the one to reach out. The request says you want to be available, to look at each other's lives when you feel like it but no pressure. Anything more and it might back fire. Not that you're responsible for her sobriety AT ALL but I would handle it with care because you don't really know where she's at in her recovery.

It can get better, it did for my family. Just be there and don't expect an apology or even conversation regarding anything that happened. Sometimes the only way to move on is to move on.