A long time ago in a galaxy far, far away....

Sunset Shimmer, the former pupil of Princess Celestia, entered the mirror hoping to find a place where she could plot her revenge and prepare to enact it.
Instead she finds herself face down in a swamp, cold and alone, lost to the machinations of the dark, that is until she comes face to face with a being almost as ancient as her old mentor, and maybe just as wise.

Spoilers in the comments
Original Art by Bakki
Featured 5/30/2019

Unhappy that her future as a member of the monarchy is denied by Celestia, Sunset Shimmer escapes through Starswirl's mirror into another world, planning to take it over to prove once and for all she was fit to rule. What she didn't expect—besides a species change—was to arrive in a world already conquered.

TvTropes Page (Just created! Needs Help!)

Art (Will contain spoilers)

Sunset Shimmer - Bloody Sunset

Spoilers Ch. 11+: Angel - Angel and Sunny
Spoilers Ch. 18+: Princess - Comic
Spoilers Ch. 121+: Alejandra Acevedo - Flying at the speed of death
Spoilers Ch. 161+: Apple Bloom - Bloom
Spoilers Ch. 180+: Food - Sunset's Party Dress
Spoilers Ch. 185+: Fugue - Fugue by Rametep
Spoilers Ch. 197+: Exhausted

(Art is always welcome!)

WARNING: CONTAINS SPOILERS FOR THE WHOLE STORY: TIMELINE

When Sunset realises that none of her human friends ever really apologised to her after the Anon-A-Miss incident, she leaves CHS to find better friends who wouldn't leave her at the drop of a hat. She eventually decides to go back to school, but is tripped on her way in and sent flying through the portal.

Instead of going to Equestria, however, it transports her to just outside of Camp Half-Blood.

Adventure and shenanigans ensue, as Sunset finds new friends and family at Camp.

Based off Percy Jackson, as well as all interrelated series, (Heroes of Olympus, Magnus Chase, Kane Chronicles etc.)

Set just after The Last Olympian.

I highly recommend you read the Percy Jackson books first so you know what you are getting into.

It had been many moons since the Anon-a-miss incident that had scarred Sunset's life and puts her friendship in jeopardy.

Now that Christmas is around the corner, some old wounds begin to reopen for Sunset Shimmer, who decided to isolate herself from the rest of her friends, for the holiday.

However, when Spike the dragon-turned-dog came from Equestria to deliver a heartwarming gift for the girl, both he and her had a little heart-to-heart talk that reignites the Fire of Friendship from Equestria.

A situation with the Dursley family gets Harry sent off to America to live with his mother's cousins, Principal Celestia and Vice-Principal Luna. Of course this brings a whole new set of problems to both the world of wizards and the girls of Canterlot High School.

Tragedy strikes the Sparkle estate one winter evening and Twilight finds herself cold, alone, and far from home.

Fortunately she stumbles across two fillies who may have more in common with her than she realizes. With no place else to go, nopony else to turn to, and no clear way back home, Twilight decides to stay with the fillies and their caretaker while she tries to piece together the mysteries of what happened to her family and why.

Bonds will be forged.

Secrets will be unraveled.

And a great journey will be undertaken.

Additional tags: Sad, Slice of Life (I don't care if it contradicts the Adventure tag, things are gonna get Slice-of-Life-y)