If it no longer changes colour, I've have some success with a REALLY low straightener treatment. I literally turn it on and off, and I have it so that I can almost stand the heat with my fingers, like it's only just too hot. I do a few strands at a time, and while it will never be perfect, it does usually just leaves a few kinks at the end of the hair.
My Sand digger was pretty bad, and now her hair is decent. It still sort of sits stiffly and clumpily, but it doesn't look as matted.