Sunset Shimmer is NOT a mane pony. Why do I know this? HAVE YOU SEEN HER BOX ART! She is a recolor of TRIXIE! Rule of thumb dictates that any "NEW LEGIT I'M GONNA BE ON THE SHOW IMPORTANT" gets their own official designs. This was true with Cadence this was true with Twilicorn. Now will she show up ? maybe she could be a bg pony or even a one off like Trixie but trust me I know important ponies. YOU KEEP THIS CRAP AND IT WILL BE COME SELF FULFILLING PROPHECY! Unless other wise stated she's not important.
Sunset Shimmer is not a new mane character. She is a TOY that happens have a lot attention cause of her silly mask. If you look at her box