Hello Sgt.
Thank you for your sacrifice and service. You put your life on the line everyday for us here at home and you have my sincere gratitude
Don't worry too much about having to change plans the two of you may already have. Most things that she may have to do she will be partly in control of when they are planned. If not, she isn't required to go to the activities, just the meetings on Sundays. She may be called to volunteer, teaching a class or chasing the nursery kids around but those aren't too time intensive and mostly during the meetings on Sunday's anyway. She may have some materials to prepare but I am sure she knows how to manage her time.
Just remember that she loves you and when you have concerns talk to her.
-SK
P.S. When you come home speak with some missionaries. They are pools of information, happiness and love.