After being locked up in the moon for so long, Luna must have had a bit of a grudge against her sister, especially after her trip to Ponyville.
I figured Celestia would be really sorry about what she did to her sister, even if she didn't say that right away 
(Trollestia on the other hand... XD )
This is just a one-shot and I wrote it in like 4 days XD I hope you enjoy ^^
princess Celestia and princess Luna belong to Hasbro ^^