Williston Northampton is a super nurturing school that has a 7-8 grade of 80 kids and has rolling admissions. We applied and liked them a lot. They’re one of the few schools that is in a little town which makes it nice for the kids to have a bit more freedom. Their list of college admissions this year was impressive.
Williston boarding doesn’t start until 9th grade. It IS a nurturing school-- but you can’t board until 9th.
It won’t be an option until high school but your daughter has The Putney School written all over her blue hair. Keep them in mind 
Quick update – I called several of the JBS recommended here. They are all clearly superb schools (with rolling admissions). I can see how fit is going to be critical (it’s like comparing 5 different, but equally perfect apples). The North Country School struck me as being a particularly good match. However, it also became clear that this may be too large of a stretch for our family for this coming year. Still, great to know that such wonderful options are out there. Thank you all again for your help. I’ll post back as things move along.
@Twining, if I were going to JBS, I would totally go to NCS. I think it’s perfect!