Warning for now: The last time I checked in the test chapter she USED HER OWN BLOOD to write on her test so clearly the manga and WN version have some difference.
So here goes:
In the WN the teacher didn't explain her reasoning but only tell him to back off.
He get pissed off, went berserk the same.
Brigitte tried to tell him to stop Aeriel, he get angrier and turned his focus on her.
As she wish inside that his rampage would have only one casualty: her, and for a moment thinking Yuri will probably call her an idiot for wishing such.
Light shone from her chest
When the light touch Aeriel's wind, the wind just disappeared leaving everyone dumbfounded.
Seeing that scene, Brigitte recalls Undine's words and blacked out.
When she came to, she's in the infirmary with the teacher at her bed side.
Thankfully there was no serious injury from this incident. There's minor ones from those who fell over or got hit by small debris.
The teacher apologized that Brigitte had got into dangerous spot to stop things, then revealed that her spirit, the Korpokkurs, actually have tunnel works under the school ground. Which is to say even if Brigitte didn't do anything, those spirits probably could've went underground to avoid the storm and took down the guy from down under.
The teacher then went on to say that thanks to Brigitte's light, this incident ended without much injuries, and talked about how the magic wave she radiated was so beautiful.
Brigitte doubted that her spirit could do that since a worthless spirit shouldn't be able to overpower a mid rank one.
The teacher suggest that maaaaybe Brigitte's spirit is just a sleepy head that hasn't woken up yet.
At this moment there's sound of footsteps, and Brigitte reacted to it.
The teacher, sensing romcom incoming, immediately go 'ara ara, I'll leave you to it then'
And of course after she left Yuuri came in.
After a quick tsundere moment of:
Yuu "Geez, looks like I was worried for nothing"
Bri "You were worried?"
Yuu "That was just figure of speech"
Bri "So you weren't worried?"
Yuu "I didn't say that"
Bri (so annoying)
Still, he's probably the first person to ever worries about her, so she was a little happy.
Then after he ask her to explain what happened
Yuu "You're an idiot"
Bri (He said it after all!)
Conversation went on and then he muttered if only they'd share the class that way he could've stopped Aeriel's rampage on the spot.
Brigitte thought about what he said, went tsundere mode and quickly push him to go back to class without looking at her face.