Since this is not said anywhere, I'm assuming this is Rarity's humanization and the rest of my critique will be based off that assumption. If it's incorrect, let me know, so I could "fix it" accordingly.
To start off I must say that pony humanization is a difficult art; I came across many pieces of the sort, most of which made me VERY skeptical about the idea as a whole. Having that in mind, I must say I'm amazed that, despite this, I'd certainly grade your vision highly; the concept is well thought out, complimenting Rarity's character as a whole. It subtly touches on various espects of her personality, making it a very compelling work.
Originality is a peculiar thing, more often then not depending on the reviewer's experience and feelings. As mentioned earlier, the concept of humanization is not new, so one can only grade the envelope such pieces are done in; and yours certainly stands out among these, giving more "feeling" into the whole. While most people stick with a simple presentation of the form, you went further, placing the character into a befitting setting, which makes the project that much more believable. You certainly deserve points for that.
Technique, in itself, is quite astounding - detailed, matured, alluring even, all of which respresent different aspects of Rarity's personality. While giving the impression of being comic book-like with the character style and colors, it's also more matured and dignified, like it was carefully planned and implemented. With a possible exception of detailed, oil painting, it's hard for me to imagine a technique more befitting Rarity's character.
The impact of the piece is irrefutable - while subtle as a whole, it strikes the viewer with a palette of stimulations, playing homeage to the character and her traits - the style and shading makes it enticing, mesmerizing even, yet still managed to remain gentle and sophisticated, playfully mixing the two extremes of Rarity's personality into a consistent whole. Certainly a portrait suitable for a lady.
Without doubt this is one of the best humanizations I've seen thus far and while I'm still skeptical over the idea myself, one can't deny the work you put into this piece. Bravo.