They managed to bring Rarity back to her senses, but not physically as she still had her nightmare appearance except for a reduction of height.

alt.

Though she returned to being the bearer of generosity she still remained the queen of nightmares, and as result, has the job of being the ruler of the nightmare forces at night while deciding to reform them by instead of causing nightmares for Equestria they're reserved for the most horrid of enemies such as Tirek.

slight alt.

After Twilight's coronation and Celestia and Luna retirement, Rarity reveals that she's still bonded to Nightmare but completely fused, interestingly she's reformed the nightmare forces by being nightmares of Equestria's worst.

optional line.

"Oh, the urges are there darling, but they've faded."