@Storyteller For one, indulge me when I 'ship' any girl with Louise. I'm afraid it will happen. I've just seen Louise as bi from the moment I laid eyes on her on screen (as it happens with most harem lead's main love interest) and since this
is comfort writing....
For another. Montmorency. Well. Montmorency is a strange case because since Louise did her a favor and then went beyond it (delivering the perfume + exposing Guiche as a bonus), she's been nicer to her. Montmorency was already pretty neutral because she's a professional who's busy making potions, selling them and studying economy on the side. She had time for a lot of bullying. Like Tabitha, however, she found Louise annoying and loud. With that incident, and helped by a dose of pity because of the failed summoning, she was pretty cool for Louise to be around the past week. She even made sure Guiche didn't try any bullshit (which he did when she wasn't present and Monmon was not happy with). So, aside from Tabitha and Kirche, Montmorency has had the closest look at Louise's recent behavior.
It was subdued but understandable.
ThenLouise succeeded and yes, Monmon was happy for her. She found the rumors rather distasteful, and pretty much reached the same conclusion the Headmaster will feed anybody who asks. Between the pressure and the shock of the summoning explosion that injured her, Louise got pushed enough that she made it.
Louise missing a day of classes which were two big sessions of Magical Theory, Louise's best marks? After the rumors, no big deal. She probably wanted to try her magic out.
Louise's subsequent obsessive training and cool attitude? Trying out as many spells as she could was more than expected. Doing it as much as she did... not so much, but it was Louise the Stubborn Mule they were talking about. The change in attitude was attributed to success. Confidence instead of arrogance and bravado. A temper cooled by the knowledge that she had succeeded.
This, incidentally, is pretty much what's going on inside the heads of nearly everybody else.
Then Montmorency finds her
dressed like a mercenary, with a
massive talking sword almost as big as she is tall slung over her back, in the capital. And she acts like
gentleman of all things but Montmorency didn't forget the way Louise was looking, no,
glaring down at her- And things just come cascading down Monmon's mental processes, trains of thought crash (and burn) and she has a minor panic attack. To which Louise, in a good mood, reacts well to, and inadvertently just mashes more buttons inside our poor blonde's head.
(Warning, headcanon ahead) Nobles, or rather mages, are descendant from a separate tribe of humans, the Markey. Those humanoids can and did interbreed with normal humans, but still a lot of their original traits remain on various levels despite the passage of time. Namely: the ability to impose change on the world, called magic; a longer lifespan; a range of hair, eye and sometimes skin colors that you could build a rainbow from; and being freaking pretty. Which is why most prettier male mages grow a beard.
That last one is normally blamed on the elves. Just don't say that in front of the Church. As much as Brimir and his tribe might have "swapped genes" with elves, it's not a good idea to mention that part of the mythos.
So: a natural androginity because of a certain lack of... female sexual dimorfic features, a cultural background that defines bishounen as the norm, a family background that makes Louise more than comfortable in male clothing... and having inherited both her mother's looks, personality and possibly curse... It's a recipe for shenanigans. Karin would recognize the pattern straight away. So will the Queen.
You should probably check midnak's PMMM/ZnT story on SB. Don't ask me the name or link, I can't remember either.