Oops....I was wrong
Yes. I would do the Love Dare. Let go of your assumptions right now. Follow the book. He will show you what needs to seen. This journey is about you and Christ. It is not about what she may have done, what the parents think, what folks at church advise. Take this to the heart...lead it to HIm in all things. Do it. Do it. Do it.
My first question is this. Are you willing to forgive if you were to find out? If so, do the dare, and allow Christ to mold you in this journey with Him. If not, do the dare and allow Christ to mold you more in His image through this journey.
But remember this. This is a journey between you and Christ, not you and your wife. If you want change, only Christ can do that. Not you.
Second. Quit trying to convince yourself. Seek comfort in Christ and allow Him to work in her life while you are working on your relationship with Him.
Read one dare a day, dont look ahead. Do not manipulate them. And I would also first read the appendix, especially the one on leading the heart.