I understand your anger and frustration at your daughter's situation. If you don't feel responsible for your daughter's actions, then in my experience it would help you to feel better to not fall into old traps such as "Where did I go wrong?" If you did the best your could, and your best was what would generally be recognized as acceptable parenting, and using those types of phrases is self defeating to your own moving on; it gives your difficult child an opportunity to blame you for her failures; and you may inadvertantly lead others to believe that either you did do something wrong, or you're obsessing with something you can't change. Whatever the reason for making statements such "where did I go wrong", they don't help anyone move on.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> I'm not sure I will ever completely let go of the fact that I am the one who...</div></div>
Your daughter will never be able to move on from this if you don't. You were young, it was foolish, and you did the best you could to get out of the situation when you were able to. It does no good to dwell on it.
You are obviously in pain. You also are obviously putting way more into what your daughter is doing and thinking and feeling than she is, or than you are into yourself. She's an adult who only contacts you when she did something to get herself into trouble and no one can bail her out. Sometimes help is beyond your reach and all that is accomplished is that she has made you upset, which gives her quite a sense of accomplishment, I'm sure. I'm not trying to be mean, I'm pointing out what isn't as obvious to someone as close to the situation as you are.
My advice to you is to let her do what she wants and suffer the natural consequences. She will, anyway, so why leave your fingerprints all over her decision making so that she can blame everything on you? Yes, this is a soft place to land. It's also a place where we get advice.