So, I guess the Equestrian legal system boils down to "No harm, no foul," including crimes up to and including treason and rebellion.
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Seriously, Trixie attacked and terrorized a town, then put a magical dome over it, assembled a throne room and hoisted her own banner.
The guile win worked, of course, but frankly, Twilight Sparkle should have galloped her way to the nearest train station or nearest other town, and either rode to, or sent a Pegasus to, Canterlot, with news that Trixie had shown up and basically conquered Ponyville, raised an army, and come back with Luna and Shining Armor to kick flank and take names.
And amazingly, after that whole nonsense was solved... They didn't punish her at all. Nevermind Twilight Sparkle's forgiving her, she should have been worried about Celestia turning her into a statue or banishing her TO THE MOON FOR A THOUSAND YEARS or something. Seriously, she did that to her own beloved little sister for attempted rebellion, why wouldn't she do that to some upstart with an amulet?
The only argument I can see in her favor is diminished capacity owing to the amulet, but even so, if she researched it enough to actually track it down, she should have researched it enough to know what it would do, so that shouldn't have been any valid excuse, kind of like how you're on the hook for anything that happens after you voluntarily get pissfaced or stoned or fucked up.
Oh well. It was still a good story, but I would've liked to see an army of those swanky royal guards march out.
[e]Also, even if Twilight didn't, why didn't Applejack say, the moment they were out of Trixie's earshot, "Spike, take a note," and inform Celestia that the town had been conquered? Even if she was in a foreign land doing something that couldn't be interrupted, she could have excused herself for a powder, telepopped back to the castle, told Luna to deal with the situation, and telepopped back.