Rarity isn't exactly what she appears to be on the surface. She's hiding a secret about herself from everypony else for fear of what others will think of her should they find out. However the thing about secrets is they have a need to come out and be revealed. After keeping everything bottled up Rarity turns to the one pony in Equestria she feels can be trusted the most.
Charlie, you've done it again.
This walks all the right lines to be interesting. It's not quite a comedy, and it's not quite a serious story, but then when you think about it, it's both. It almost fits in with Rarity's character too well. It does a good job of dissecting a character while remaining silly. I think that's the best skill you've demonstrated so far in your writing.
Anyway, keep it up.
BOW-CHICKA-WOW-WOW!
...I am a horrible pony.
An enjoyable tail!