no regrets... just do it...
OK, I just sat here and read this whole thread. My opinion of what I was going to answer is unchanged.
Straight up...
You tell her.
Pour your gutts out from the heart with everything you have told us right here. If your soul says cry. Do it. Hold nothing back. *Including* what your "head" logically tells you to do also as you have posted.
No regrets, my friend.
Why?
Story for you...
Btw, I hate these kinda stupid chain emails you get from friends to forward etc. This latest one I played along and answered. It was a "get to know your friends better game". Fill in the blank, forward your answers, next buddy reads, adds their own, repeat.
Here was a striking question: "What are you most afraid of?"
My reply: "Dieing with regret".
As part of my professional background in healthcare, I literally DID watch people die with regret. It's difficult to even find words to describe the depth of that experience.
If she doesn't want to see you, hear it, etc. That is it. You tried. If so, you do what I said earlier.
If she is meant to truly marry this man she is engaged to... what you have to say will not change that.
The outcome is unforeseen.
Lastly...
FWIW, when I personally was in this same situation, a wise friend said "to chance is to live". With that, I bared my soul. It did not change the outcome. But I will not die with regret and eternally wonder "what if"... so, regardless of outcome, I'm at peace.
Good Luck!
Miranda