^ That's a good point about Indou being even more in the dark about "maidenhood" than we are, and maybe suggests why its status keeps nagging me (more than it should for its role in the story, I think).
In many schoolgirl lesbian stories (often even ones of the 404: Men Not Found
genre) there's no established cultural space for girl-girl love, and the central problem often is finding a way to overcome that or to create a personal way it can happen for the main couple.
But here it's like lesbianism is practically an approved club activity already (I'm exaggerating, of course, but not entirely), but Kagami keeps rejecting it. Your idea that Kagami is refusing the "maiden" option because her feelings go deeper than that is pretty convincing at this point, given that we aren't yet sure what "that" (i.e., the maiden status) actually is.
But you made me realize that there's a part of me that wants to say to Kagami, "Just go ahead and make Indou your maiden and get down to business, fool." I'm confident there's a good reason why she doesn't do that, but right now she remains almost as much a cypher to us as she is to our Little Hamster Cadet of Love.