I'm honored.
She could totally wear black dressage tack. *ponders* Her color spectrum of choice would be white, silver, light blue if you needed another color for highlights or something.
Aww, you're a love. I'd rather you didn't adapt it into a real horse marking; the shooting star is kind of her thing. xD She isn't really of this world, and a shooting star marking makes sense in her context. It isn't painted on, it's just a marking she was born with. She's actually from a line of mages (she originated in a long role play / story I wrote with a friend of mine) and it was taken as an omen for her house.
I did a REALLY rough sketch (just grabbed some random lineart off the internet, lol) to approximately show you what the other side looks like:
img.photobucket.com/albums/v70… It's just the shooting star tail, and would probably be mostly covered by her brow band, so you could draw her from that side and avoid having a random weird looking mare other-worldly mare in your comic.
She's not actually a known breed.
(Aren't I helpful?) An Arabian is just the closest I could approximate, since she's small and has a wide, dished face. But she wouldn't have the high Arab tail carriage or the throat latch. She's really more of a large, typey pony.