If the rebels against Nightmare Moon's rule wants to get rid of her, the solution is simple: kidnap her father, place him deep in a narrow mine, wire explosives in said mine. When she comes in to rescue him, BOOM! Problem solved without having to fight some-pony who would obviously be one of the strongest soldiers available to Nightmare Moon.



Of course, if the father cooperates with the rebels willingly, an extra step would involve teleporting him out the moment the explosives blow, but that really depends on whether or not he's a dissident or loyal subject. If latter, he's expendable.