You could try any felted bag pattern, and use intarsia to knit different "blotches" of color....
WOTA colors: forest heather, amber heather, grass, avocado, evergreen, fern, chesnut, coal and mist might work. Check here
I've actually found the perfect yarn (cascade 220), all the colors are the perfect greens and kaki (I can't spell), but I'm really not sure how to work it. I don't want to mess it up. Since I want to make it for a present if I mess it up, there goes my budget for buying her a gift.
And inertia seems a little bit out of my range of knitting skills right now....