Oh she's gorgeous! She looks like she's doing exactly what my app mare did, she was born pure brown and changed into all the colors she is now (see avatar).
It's called Varnish roan, it's different from regular roan, the giveaway is the lack (or less) of white on the "bony" areas, her hips, sides etc. Varnish roan also affects the face and head, whereas regular roan doesn't. She may also have some snowflaking, but that could just be the varnish. I love Apps and have done a lot of research on the color genetics. There's no telling what she could end up as, she could stay looking like she does now or she could end up almost completely white, she could even get spots!