OK, 1TmakesnoSence..... Were you raised in this? Even tho you have mentally gotten out, that doesn't mean she will ever be out in the same way that you are. Please, please, please do not do this to yourself.
I have seen so many people 'leave' the witnesses, be DF'd, not want to be one, didn't 'really' believe it... but still? something in the back of their head kept saying "maybe the new order will come".... One guy was going to marry a 'worldly girl' (he had been out, DF'd for years) but couldn't... he worried, "could I really give her the life she needs?" He still thinks about going back BECAUSE he wants to visit his brother.... He just stinkin' wants to play golf with his elder brother... so he thinks, "Maybe I should get reinstated so I can play golf with my long lost brother." Shunning, family, losing life is very difficult for anyone to endure.
Your girlfriend is still pretty young... she is still probably pretty close to her mom, right? What about her dad? sisters? brother? Family, shunning and ALL THAT ROT/ BLACKMAIL can change people.....it's hard.
Give both of YOU a break... Who wants to fight for half of your married life of "what you will and won't do"? Marriage is hard enough when your both on the same page, right? Surprisingly, you may just find another person you love as much, if not MORE.... That has happened to people over and over also....
Be fair to yourself, and her..... Maybe you could "call if off" for a year? then see where she stands... Let her decide without pressure... When anyone gets off the "hamster wheel" (no matter what it is) you can get a view of life from a different perspective.
Take care, take time.... be fair to the both of you.