She is defiantly Not a buckskin,
I no doubt would call her a wild bay.
That is when a normal bay has legs that don't extend as high up as a classic bay, resembling the wild ponies that are bay, this also caused by 'pangare' (also called mealy) on them, which she has, the light areas on her soft spots (nose, armpits, flanks).
This would probably be common in a thick native pony breed which she appears to be. If Icelandic's are common around there, then it is very likely she is at least part one.
I can't really define anything else, I am not good at those breeds of pony / European types.