Breed? Looks silver buckskin to me, but silver isn't in a lot of breeds. Is she gaited? Many gaited breeds have silver.
I test through Animal Genetics
To REALLY know, you'd need to test extension, agouti, cream, and silver. Would be $90 for all four. (they do an extension/agouti combo for $40, the rest are $25. You just pull out some mane or tail hairs, really easy to do).
If you want to be cheaper, I really don't see how she does NOT have one cream gene. So you could skip that. No way she has two, her skin would be light and her eyes blue. She is also not champagne. And really it's obvious she's not black, so you don't NEED agouti (if she is "black" than she has at least ONE agouti gene, which makes bay). So if you test for extension to determine if she's buckskin vs palomino, that'll tell you a lot. If she's gaited, and she comes back buckskin, it's more than likely that she's silver buckskin.
Basically, if you REALLY want to know, 100% without a doubt, $90 for the four tests I mentioned. If you want to go cheap and just have a VERY good guess, $25 for extension.