I can't imagine how I would handle this, but I can sure see where you are coming from, DH -- BTW, "dinged" is an understatement, right??
You're doing all you can do. Just don't let it take you to a homicidal level. At least no one was physically injured, and no one intentionally hurt your daughter, that is one thing on the bright side. Some kids suffer and survive lots of horrible sexual abuse -- she will be okay, with the professional help you have provided, I think the damage control will be really effective.
People do dumb things. People make dumb mistakes. But as long as there is love, I think it can overcome even the most wreckless behaviors. Maybe your wife got drunk on sex -- NRE -- people do some crazy things when they are drunk... crash cars and kill people, even. Underneath it all though, she is a loving person. I believe that love will prevail. Your family is going to come out okay, because you were all trying to keep the focus on LOVE. Don't lose sight of that, friend. You are a good guy. Hang in there.