I know I'm kind of late to the party, but for what it's worth, I'm really sorry that happened to you. I can see your pain and personal confusion and heartache in your post and I sympathise deeply. Lately, I worry that my story is going to go down the same road as your's...
But, we can't let our fears guide us, otherwise they'll take us exactly where we're afraid of going.
You can't control how she feels. You can't control what she DOES. It's unfortunate that she felt unable to be open and honest in her relationships, but at the same time...like I said...nobody can control how she feels. I'm sure you and he did all you could to try and ease her mind (and if you think you didn't, learn from the experience).
You didn't do anything wrong. You are not a bad person, or a bad poly lover.