Flood the brain with porn to force her blood pressure down?
You have my utter respect, Ojou-sama... won't work, though.
In my eyes Kanaria is what I would call a "capable failure", in a cute way. I like her quite a bit.
Her reaction is understandable. Put yourself in Kanaria's shoes and think about that world:
That girl is a wealthy Ojou-sama with a good family background. She's widely educated, well-mannered and a trained male guard student, so she is considered "safe" - of course we know what's going on inside her head, but for others she shows a poker face. Don't forget her grade ranking which is pretty high. Not sure how many classes the second grade has in total but A, C and E got mentioned so it's at least five - if each class has 39 girls and Kanaria is among the top 10 overall it shows where she stands in the pecking order. And, incase you forgot, this girl has another major asset: Compared to Sou's other guards, she has a small build with a modest amount of "useless fat" on her. So her appearance is less likely to inflict fear in men, which would be considered a desirable trait in that world. Sou is non-standard, but she can't know that yet.
Kanaria can think of herself as a premium catch and wouldn't be too far off.
Now a really hot guy like Sou calls her hair beautiful, which basically means he approves of her looks to a degree where he would say something like that - no sane man would ever do this unless he means business. If you take that into account and go by the world's standards, then he okay'd her as a future wife candidate. Mr. Oblivious really did a number on her with that one line. That she maintains her sanity even later on instead of going bonkers like others is something to respect.
On a more personal note - with such a distracting and shiny, golden mane glistening in the summer sun right in front of me I might have started blurting out similar stuff as well. Nice job.