What a fabulous idea!
You and Mom should both wear tiaras (and maybe even a fancy homemade sash?) to celebrate the occasion! I love the purple theme for summer!
You're never too old for bubbles. Hand out small bottles of bubbles to all of the guests.
Do you and your Mom have favorite poems? Maybe you could have some guests read some of them. Do you keep a journal? You could go back several years and read about where you were at that time in your life as compared to now.
Buy or make 2 "autograph" books to pass around. Ask the guests to write something in one for you and one for Mom. You will have this to treasure and look back on! You can update it with pictures afterwards.
I can't wait to see the other ideas people come up with!