Since she didn't die right after weight I would guess it was not due to blood loss, maybe a blod clott. If the babies are healthy an enfection could have taken them too, so that's a long shot. I had the same thing happen to my female Hammy who was in perfect health weeks after she gave birth. When her babies were almost weaned she died, I am guessing the babies sucked her dry and she did not drink water for a while and she just dehydrated and died.
:I would bet that she either just plain wore herself out after lost blood and all that or she had a secondary infection slowly work through her. Are the pups okay? Or are they small and bony? Then I would suspect infection. :Sonya