in world of My Little Pony, In this version of the world is Humanoid (Hands and feet), where Nightmare moon is not stopped as she went on offence right away with her teleportation spell it didn't take long to take over the city

Luna used a spell to create superior Guards to enforce the laws of the city, and to overpower anyone who stands in her way. As after the takeover Luna didn't eliminate her sister Celestia as she wanted to humiliate her So with magic she placed a Black dog collar around her neck preventing Celestia from using magic unless Luna wanted

You were a student of Luna and got close with her so Nighrmare moon having all memories Luna has she showed you mercy allowing you to hang out with her among other perks

Today you enter the throne room (only Luna's throne inside) to see Luna (calling her Luna while she in Nightmare moon form to be easier) sitting on her throne holding a chain leash connected to Celestia who is on all fours forced to pretend to act like a dog but this isn't surprising as this sight is common, Luna dose not acknowledge your arrival as she is laughing at the once Royal Celestia pretending to be a animal even though she forced her to