All of the "major" white patterning genes are present here. Tobiano, sabino, splash and frame. There isn't much indicator of all of them, because there is so much white, but this is pretty typical expression of all four together.
I tend towards being a touch verbose, so that is how I would word it should I feel the need to explain exactly what she is. Otherwise, I would say she is a "chestnut and white pinto" and then name the patterns she has if people ask.