Wow, that's a doozy. I would let her know that right now, you don't need any help planning, but when you do, you will definately let her know. I would then find some little odd 'n end jobs to have her do, that way she feels important and part of the planning, but you are still having most of the control. For example, let her pick out the guest book, it's probably not really all that important to you what the guest book looks like, and she'll feel important for getting to pick it out. Just build it up, "You know xxx I would really appreciate it if you could help me out and pick out a guest book for our wedding." It sounds a little like something you would do with a child, but it may work with her.