Moving to another world means you get to leave whatever you want behind. For Sunset Shimmer, that will always be more of a blessing than a curse. Now, one conversation over tea will set in motion the future of two worlds.
Ever since Twilight Sparkle has taken the steps to princesshood, Ivory Scroll has become obsolete as Ponyville's Mayor-Mare. Nothing could be more devastating to her, and she aims to renew her sense of purpose in the world.