I'd like to first start out by saying that is the most cute picture of Twilight I've ever seen. Anyways, now to be serious.
Your strokes are very smooth and clean. Though the lines in the tail just seem to be a little over arched a bit. The tail all together seems like it could of been done a little slower, and taken a bit more care. Her rump too looks a little bumpy, though that could be due to the lines being a little thick and causing the perception of it being bumpy.
However cute it is, it's not an 100% original idea. I've personally seen many other pictures of Twilight hiding behind books and such. But still very, very cute.
Overall when compared to all of your other drawings you seem to be very consistent with your style and technique, and every last one of them are very well done. The style does sort of remind me of Lauren Faust's style.
Overall I'd give it an 8.5/10. It's very well done with fairly consistent line thickness, and being very smooth (minus some areas in the tail). Keep up the good work!