She is a flashy color because she's graying out.
I researched Aztecas a bit, because it looks like the horse is in Mexico(?), so I figured, why not an Azteca? But Aztecas are supposed to combine Andalusian, Lusitano, Quarter Horse and Criollo, and to me she doesn't look like any of those breeds.
To me she looks like a Thoroughbred. I guess she could have some QH in her, but I really don't see it. Maybe that's just because she's thin.
She has a really pretty face, almost like she has a little Arabian in her, but the rest of her does not look Arabian to me.
So my best guess is Thoroughbred.
She will look so pretty when she gains a little weight. She's going to be a looker.