Image imported from derpibooru
Original Description:

Through the portal came a tall mare… Standing on her hindlegs? As she stepped through, she collapsed down onto all four of her hooves and looked around. Flurry Heart quickly stepped up to her in excitement- “Sunset Shimmer!” She exclaimed, “Remember me? I was only 3 when you became an Alicorn!” Sunset Shimmer took a step back in surprise- Flurry Heart wasn’t somepony she saw often, seeing as Sunset and the Crystal Family almost never are around at the same time, so seeing Flurry Heart fully grown came as a bit of a shock. Flurry was right, the last time the two saw each other was when Twilight pronounced Sunset as the Princess and Protector of Dimensions. It was still so weird- I mean, back where she came from, she was merely the vice-principal to her world’s Twilight. That’s when Luster Dawn and Trixie stepped in, recounting everything they’ve found thus far. Sunset was eager to help, of course, having told her world’s Twilight to create an alibi for her being ‘sick’ as she came to this world. So the team to help Starlight Glimmer expands, and Trixie reassures Luster Dawn that with Sunset’s help they’d find answers…

Sunset’s here! With her experience with dark magic corrupting her, this should make their job a little easier! Sure, they could’ve asked Luna too, but she doesn’t have the same connection to Starlight so Sunset was probably the better choice.