I’d say headbow- it’d be reminiscent of the large bow on her school and senshi uniform. As far as the brooch goes, which one did you have in mind specifically? I’m sure you could find a multifaceted gem to use in one!
The Super Chibimoon brooch (though I’m sure you know what it looks like!)
I think the biggest problem would be finding a rhinestone big enough. I’d probably want it somewhere between 5-7 cm wide at least. I have no problem using Model Magic or something to make the housing myself.
I really want to make a heart pouchette to go with it, too. Maybe just a red one with lace around it so it matches the skirt even when it’s in a non-themed coord.