hun you can not blame yourself. I dont know much about the rodent department but from what I understand is there arent many vets that know how to deal with rodents. So being as they are so small price goes up.
Do you know who the father was? Could he have been closely related the the mother like a father or brother to her and he got a hold of her? This could lead, as I said, to problems. Sickly, problems along with others. I ran into a sick couple who bred dogs wrongly. They were really inbreeding their dogs like crazy. We had just met a couple that just got together and the guy was inbreeding his dogs bad. The gf knew it was wrong but we couldnt talk any sence into him. Well his female was bred with her brother and she had a large litter of pups...11 if I can remember right...it was a large number... well...all but 2 died...because the inbreeding was that bad.
Though it is understandable that you didnt know. I havent done rogents so I dont know how they work.