
Primary inertia isn't something you can spot, they simply don't go into labour, the bitch may be happy and eating as nothing is happening to upset her.
http://www.champdogsforum.co.uk/board/topic/137551.html#fp A thread which resulted in a c/section and 2 healthy pups.
The placentas are only meant to last a certain number of days after that they start deteriorating and the pups die,they maybe moving around one minute and dead the next[ I experienced this last year and she went into labour 2 days early and had one fresh still birth and 2 partly decomposed pups who had died some time before, she had slept next to me the night before and I could feel puppy movements, I wouldn't wish this on anyone, I hadn't done anything wrong, the labour was short only 4hrs to my other girls nearly 24 hrs from start to finish]
An Xray will show the bones very clearly if she is due as well as showing how many pups and their head size compared with the dams pelvis.
I truly hope that things work out for your bitch and her pups.