I hope all is O.K., I came across this article about premie pups, i know that is not your main concern right now, but you might get an idea of different care or something. I think it could have been some formula, but you can't know that for sure. She is very fragile either way, so no need to blame one thing or the other, just nurse her the best you can and hopefully it will work out. I will say a prayer for her.
How To Care for the Premature Puppy - by Roberta Jamieson