I've no clue but it must be really sad for you.
I'm so sorry you have had such a difficult time. What are you feeding her? I also heard about using folic acid, don't know if that would help or not.... I belong to a breeding group thru yahoo and someone on there might be able to help. This is the link...
CanineReproPuppyCare : Canine Repro & Puppy Intensive Care