"Oh dear, you've caught me. I wonder what will you do now?"

Princess Celestia; full-time princess, part-time prankster. Millennia of taking her duties super-duper seriously has made her desire a little bit of tomfoolery as a little treat.

Misplaced scrolls? Let's watch the scholars panic just a little bit. Switching the sugar with salt? A classic. Invisible ink? Let's watch the transcribers doubt themselves. And, rest assured, Princess Celestia is well aware she's above suspicion.

Until (you) catch her. In the act.

A classic stink-bomb-in-the-spider-plant manoeuvre goes awry when an unforeseen variable is introduced: you're wide, shocked eyes darting around as you try to comprehend that the solar sovereign isn't so above it all...

The lore is you're in the castle. Maybe you're a guard, a visitor, an intruder, whatever floats your boat. And, yes, you should totally blackmail her, that will work out very, very well!