Accept it already, she will never appear in the show.

I prefer Sunset Shimmer over Starlight let’s-mess-up-time-and-destroy-Equestria-and-ponykind Glimmer. At least we actually saw how Sunset tried everything to make up for what she did. Starlight on the other hand just “apologized” and they all became instant best friends. Instead the mane 6 should have sent her away on her own quest to actually deserve to become their friend. There would have been enough time in season 6 for her becoming friends with the mane 6

Oh well, not like they need a ninth wheel on this Stupid Train.

Not sure why Sunset would be envious or feel left out, she only knows one of those Ponies(Twilight) and Spike. Sunset is still the superior character to Starlight, however, and unlike Starlight, has a unique design not stolen from Aria Blaze.

Sunset has a whole world to oversee as it becomes progressively more magical. She’s got enough to worry about as it is.