She is palomino tobaino. She may have a little bit of countershading. Tobaino, or the overo genes can act on ANY base color, as with any white pattern- rabicano or roan included.
Palomino is a chestnut horse(red based) with one cream gene. Cream is a dilution gene, and it lightens the coat. [bay + 1 cream is buckskin, black + 1 cream is smokey black?, chestnut + 2 cream is perlino, bay + 2 cream is perlino (<3) black + 2 cream is smokey cream?]
A palomino is essentially a chestnut that is heterozygous for cream, and a cremello is chestnut that is homozygous for the cream gene.
Palomino can be light or dark, but is all genetically the same(as with sorrel, flax. chestnut, and red chestnut). It can range from this
to this: http://www.mustangs4us.com/Horse%20C...0&%20filly.jpg
Remember, palomino is a golden(or light cream color) with dark skin, and a pale/white mane and tail.
Also remember, the horse is palomino with white (tobaino) markings, not white with a palomino patch.
If you can, get the horse and spray her down, you will notice where the white patches are, there is pink skin; where the palomino color is, there will be dark or black skin.