Not the the mane six. But make her a needed character like Apple Bloom or Celestia.
Well, now that I think about it... It would actually make sense to put her with the mane six. For one, the point of the mane six was equality and balance in power. Which is why there were two of each race. And like Twilight in the beginning of the series, Sunset Shimmer needs to learn more about friendship. And is sent somewhere she is unfamiliar with anypony. And it would be interesting to see how the mane six (excluding Twilight) would react to her. Maybe they'd be overly friendly and hit it off more than Twilight had originally interpreted. And she may feel like she's being replaced. If they made that the premiere of season 5, it could be while some kind of dark magic is flooding throughout Equestria. Which is also a reason that Sunset Shimmer is there. Celestia might have called her there to help fight it. And when Sunset shimmer gets into Twilight's head and she becomes jealous or hurt, the darkness finds a weak spot and takes control of her. Like with Rarity in Inspiration Manifestation. Does that make any sense or am I just rambling?
Also, I wouldn't want her to be apart of the mane six permanently. Just have her for a premiere or something and bring her back every now and then like they did with Discord.