After Moonstone lost her horn, Twilight asked Tempest if she could be the captain of the Royal Friendship Guard; she figured it might help Moony to have another unicorn with a broken horn around. She didn’t mention that there really wasn’t a “Royal Frindship Guard” until after Tempest said yes. Luckily, with Tempest came Grubber and a bunch of Storm Creatures who were delighted to get a job in Equestria (the party held the first time they were there really left an impression), especially since the job description was basically just “stand around and look intimidating”.
 
Later, Twilight also asked Tempest if she could teach Moony some self-defense, which she immedietly agreed to. After all, she had had no problem teaching Storm Creatures how to fight, and they were bipedal! So how hard could it be to teach a foal a few tricks?
 
…She may have to re-think her strategy. And find her a lighter opponent to start with.