That's not a bad idea, actually, although it could potentially cripple her more so than Olimar's Pikmin being hittable, since Olimar can have multiple Pikmin, while Rosalina only has one Luma (save for my idea of her Final Smash). Would giving the Luma its own hurtbox balance Rosalina? Perhaps, but it could also hurt her at the same time. I can still see where you're getting at though, but the way my Rosalina moveset plays, giving the Luma a hurtbox would make her potentially worse unless I do some pretty significant changes, and considering how far into her moveset I've committed my time into, I don't really want to do anything major, at least not right now. That said, if you have any ideas of a moveset that can implement such a system, then feel free to post it, and I'll be happy to add it to the OP.
Thanks for the feedback.