So, I finally got the chance to sit down with my younger cousin, and watch the season three finale.
She went into it completely unspoiled, not knowing what would happen, and when it came to the moment of truth with Twilight and Celestia in the astral void, well... initially she seemed more focused on cracking some jokes about the poses not looking very natural for an equine body shape. However, the moment Twilight started rising into the air, glowing with inner light, my cousin's eyes lit up just as much and she was a flurry of, "Oh my gosh, what's happening!" and all I could do is smile as I watched her watch Twilight.
Then Twilight lands back in Ponyville to spread her wings for the first time and as she does my cousin was practically leaping for joy, which only doubled when Celestia showed up to proclaim that Twilight had not only become an alicorn, but a princess as well. This is something my cousin had asked about way back when we first started watching episodes together last summer. Even as early as the end of the second episode, my cousin thought Clestia must be training Twilight to become a new princess, so I knew she was going to enjoy this, but getting to see it all play out on her face was a real treat.
For all the drama this finale caused in the older peripherals that make up those of us that call ourselves bronies, it was good to see that at least for one young girl --just a few years over the show's target demographics-- this epic event went off flawlessly... well, almost.
She was very concerned that this meant the show was over, that there would be no more stories left to tell, so it was also nice to be able to assure her that a fourth season was already in the works.