I'd be a b).
It will probably be nice to see her and feel part of an occasion, and you will have another little story to tell people. Not knowing what kind of event it is you are attending, you might only get a brief glance from her on the day, but it will probably still be rewarding just to have been invited and seen her.
I stood in some line that the Duke of Kent walked along, and various royals of greater or lesser importance have landed on our school playing fields over the years, so I've probably seen glimpses of a few, but never seen the Queen. There will probably be some photographer following her round I'd have thought, so you might appear in a picture later, often get posted up online I think.