Well, you eat an elephant one fork at a time. I would just sit down to whatever is close and start folding. Once the larger pieces are folded, they will be easier to sort into colors. Or, another method may come to you as you work on it. But, be forewarned, if grandmother doesn't want it organized, it will end right back up to the way it is now. It happens so quick. It always reminds me of the line in the poem that goes, "something there is that doesn't love a wall". It doesn't love organized fabric either.