This picture now begs the question: What will you do if you encountered Flandre inside a secret room/shed/closet/garage in your home.
Depends, do I actually have the meta-knowledge about her?
If not, probably everything you would do if you found a lost kid anywhere.
If yes, swear a lot, lock and barricade the door and do anything to contact/summon/piss off Yukari/Hermaeus Mora/The Lady of Pain and if that didn't do shit. I'd probably repeat it only aimed at the nordic/germanic gods since Loki probably wants his woundstick back.
I'd say that's overkill, but in this case I'm agree with you.
More that Yukari/Hermaeus Mora/The Lady of Pain have a remarkable amount of overlap. My money is on the either being the same person or just different aspects of the same being.
And its not so much overkill as it is to get rid of her before she makes me/my belongings/my home disappear by means of kyuu~-and-boom
What you guys fail to predict is that locking up the shed may only make her angry. Why can't you just approach her catiously yet friendly? She's not bad as a person you know.