My first thougt was to return it but then I thought about it more. If I had to return something valuable then I think I would also give her every little thing that was left behind. "Here's your gold coin, your dirty old mattress, and 3 broken vases". Its yours, you bought the house and the garbage left behind, doesn't matter if the garbage happens to be worth something. Consider it a cleaning fee.
Edit: Just noticed the part about 3 years...ya, its yours!