That Walker was no where near bloated enough to have eaten all of Lori. And where were her bones? T-Dog had at least three Walkers chowing down on him and they still found his remains. My money is on Lori coming back as a Walker at this point.
There's nothing to show that the walker we saw was the only one who chowed down on Lori's corpse. Just that he would appear to have gotten the lion's share and was too full to stand up afterwards. As for where her bones went, well... I have no answer to that one.