I found out how she bugs out, because it just happened to me.
I got mind controlled from one of the satyrs close to her cage and started attacking her, after the mind control wore off, she ran back to her starting position inside the cage.
The quest wasn't failed, but she is now stuck and after abandoning the quest, she won't re-issue it to me, or any other player for that matter.
Yes, that's because you found her in the bugged/stuck stage I described above. I had the same issue yesterday, but when I came back to check on her today after the server crash and restart, I was able to turn the quest in to her and start her escort.