Thank you everyone. If I flew there, I'd be out $1000 and I'd have to flake on a friend for something I promised I'd help her with. Short story - I'd give up my own needs for hers. I think the letter is the way to go.
I'm going to call her today and tell her I'm proud she made the choice to go to recovery (I am) and that I have so many things I want to do with her when she's sober. And I'll tell her that I wrote a letter and put it in a box with some photos and sent it to her rehab facility. The letter thing might be better anyway so she can read and reread if she needs to. And hold onto it if it helps her.
Thanks again.