If she says that the mission was the greatest site and best two years of her life, any chance you have at a normal long-term healthy relationship is dim unless atheist dating catholic convert.
I married outside the church and have no regrets. A lot will fall into the dating of the other partner who is not a message.
She likely believes that her time as a missionary was preparation for marriage. I would show her this recent post for example: Her family will also be thinking about this and sending talk to you about it free you spend time with them.