Should have burned, rather than buried, his body
She's been stuck there 13 years, not sure how long she lived there before she imprisoned him. Now she's free, seems like she'd want to distance herself from the place. So she sells it, new owners want to put in a pool, start digging .....!
Just put his dead body outside, then lay lots of gas soaked wood/boards around it, and light it. Fiddle with the pile til all traces of him are gone.
Now, no evidence of his body! She and he are free, at least of physical evidence.