Well, Sunset has never actually turned into an alicorn. If you're referring to Daydream Shimmer, that was more of a powered up form she briefly obtained after absorbing all the magic from her friends. So that wasn't a form she herself achieved, just a temporary powered up form, similar to what happened to the Mane Six when they defeated Tirek.

As for Sci-Twi, my theory on why she has an alicorn ponied-up form is due to how she got her magic. The magic in Twilight's crown was alicorn magic. She shared that magic with her friends when they defeated demon Sunset, and the magic stayed with them after she went back to Equestria, which is why they still pony-up. Some of the magic Sunset gained when she became a demon stayed with her as well, only now it was uncorrupted, which is how she obtained her pony-up form. Sci-Twi absorbed the magic from all the EQGs, the equivalent of alicorn magic, which is how she gained an alicorn pony-upped form, but she herself didn't earn her wings, which is why she was still a unicorn when she went to Equestria.

So what's you're animal opinion?

