Rigor tends to relax after a while, 72 hours average according to Wikipedia, so I wouldn't say days - rigor is a sign of a relatively recent death. When my cat died, she started stiffening up after about 45 minutes in the large joints, and we couldn't bury her until the following evening in a family member's garden, when she'd already become a bit more flaccid. Not a happy memory for me, but first-hand experience that the dog could be stiff after only an hour or so. The maggots are a bit more worrying but again, if she had flies in her flat already, and the dog had evacuated on dying, they would be all over it (like the famous saying) within a short period.