Quite possibly she was too young or not in good physical condition or just plain stressed out and that caused her to abandon her litter. I've gotten preggie rats from stores (either they didn't appear pregnant or in one case it was a rescue due to the living conditions of the heavily pregnant female rat) and it's often not a great outcome. Really young females of any species are often just not equipped to handle a birth. Hopefully she'll do better for you the next time around. Let her rest up a bit, feed her up well and then see how it goes.