I always give them a chance with their first litter. While mothering is instinctive, it's only PARTIALLY instinctive--they often do need practice to truly become good at it. It's not at all unusual for a first-time mom to neglect her litter, or have problems caring for it. Most of the time, the second litter is fine.

If it's NOT a first-time mom, then it could just be a defective litter, and she's not caring for them because she knows there's something wrong with them anyhow--there were stillborns in there, so that's far from impossible. As with the first-time mom, I'd give her another chance. If it happens again, she's snake food. No sense in killing off a perfectly good breeder rat for just one bad litter, after all--it takes time to raise them up to that size.