Just be polite as you would be with any other visitor. She won't expect you to be an expert on Japanese culture any more than you expect her to be the other way around. Ask her questions and listen to the answers, make sure you have local information to hand for when she may like to see the area or going sight-seeing and make sure you consider her food preferences etc. and find some nice places to eat out. Be yourself and be relaxed and i'm sure you'll both have a lovely time.