Great question Mam, and great responses from everyone!
I haven't even thought about telling dd7. I figured DYS would be more of a behind the scenes thing, with me getting and implementing advice that I can bring to the school.
But it's true, I would like to meet some local families and participate in some events, and then there will be some 'splaining to do!
My situation is complicated by having an older dd who has all the gifted intensities, but not the pure academic strength of my younger dd. It will be a constant balance to make sure dd7 has all the resources available to her, without having dd9 feel like "less."