
Personally I'd get her in for a C.Section at full term. At least if that's done, you'll know she's been 'cleared out'. So the puppies she delivered were premature and didn't survive?
I had one of mine who seemed to be pregnant at 5 weeks, but didn't get significantly bigger. She probably reabsorbed some although when we had to go for a C.Section to get ONE large puppy out (typical but at least it was a bitch) there was no sign that she could have had more at one point. We have never had a miscarriage like you've had to exerience.
Be guided by your vet with this - provided you know and trust him!