I had a roommate for a couple years, who was and still is one of my best friends. One time I got home from a "business trip" to New Orleans and found the kitchen a disgusting mess. The shit smelled so bad it gave me an instant gag reflex when I walked in there.
I'm not a neat freak by any means, but after flying hungover in a plane for three hours, I didn't need to come home to that. I got a couple of hefty bags and chucked away all his shit he didn't clean up. Pots, pans, dishes, silverware -- everything. At the time, I don't think he cared for that too much, but at least we can look back at it today and laugh.
If I was your friend I'd just start throwing a bag or two of that stuff away every couple days. Chances are she'd never never miss it, and if she asked about it, just play dumb, or say the dog pee'd on it and it couldn't be saved.