...my hope is that she is able to 'break the rules' and date me. secretly, of course.
....i'd honestly marry this girl.
.... how would I even begin to talk to her?? .
Just so you can see this clearly, you already talk to her on a regular basis.
You cannot honestly be ready to marry her and not be addressing the issue.
I am sure you mean, "How do I get her to understand the truth about 'the truth' ?"
Just her dating you gives hope that she is on her way out. But you have to put up
with the guilt and the back-and-forth feelings she will have.
I tend to give standard advice. Here it is: read COMBATTING CULT MIND CONTROL
and RELEASING THE BONDS from Steve Hassan (freedomofmind.com or Amazon)
and get her to read CRISIS OF CONSCIENCE by Raymond Franz, former member of
the Governing Body of Jehovah's Witnesses (commentarypress.com).