I was afraid too. I am married and it popped up out of no where. I was extremely lucky my with already had the vaccine.
Sadly, odds are if you have already been having sex, she probably has it. She could be lucky and fight it off, then maybe get the vaccine.
Regardless, if you are marrying each other you both love each other through sickness and health. Just talk to each other, educate each other so you both know it's really not the end of the world. Just have to deal with a hurdle now and then :)