She looks like a chestnut overo+sabino to me. As for the white hairs, she could be graying. Very beautiful mare!

I agree with Dimrill Dale. Maybe even sorrel instead of chestnut. :)

Sorrel is the same thing as chestnut, so you know.

I'm not sure about sure about the mare greying out, it'd depend on how old she is. The white hairs might be a result of the sabino, since a lot of sabino horses will have "sabino-roaning", but the horse doesn't actually have roan.

She just turned 14, so I don't think she's going to grey because wouldn't it have become more obvious by 14?? And thanks all for your comments!! <3

Nah. She would have already greyed out by that age. So, I'm firmly going to say that the white hairs are a result of sabino.

She is mysterious colour, it's maybe dark chestnut sabino or brown dun sabino but I'm not sure. Very beautiful horse!

I don't see any evidence of frame or grey at all. Both the roany effect and the spots are typical of sabino. I also don't see any evidence of dun or black base - she appears to be a typical chestnut base.

I'd say she's a plain old chestnut sabino, no strange modifiers or other patterns involved.
She's actually fairly typical of a chestnut sabino:
http://www.horse-genetics.com/Windsong-Firefrost.html

I think chestnut sabino.