I have watched people I thought were "good" go back out more times than I can count now after 5 years in recovery. Not all make it back. It's a horrible helpless feeling. I felt some pretty substantial grief and guilt when one of those people, someone I had known since high school and had had a pretty serious romantic relationship with a few years ago, lost his battle with the demons and committed suicide in October. He got sober (for at least the 3rd or 4th time, I don't know for sure) a few months before I did. Went back out about 3 years ago. I knew he was out and I tried so hard to reach him. I kept hoping he'd listen to me, that he was worth saving and that I cared and wanted to help. He didn't believe it, I guess.
All we can really do as bystanders and fellows in recovery is to keep trying and keep in touch. I wish there was more I could have done, I still cry about it.
Just let her know that she can lean on you if she wants to come back.