How old is she? Is this her first litter or has she had many before? If bred too young or too old it greatly increases the chances for bad litters. I definitely would give her a month away from the male (if not already separated) and if on the young side, maybe two months (rats breed best after 12 weeks of age though should be retired around 14-18 months..depending on whether they have back to back litters or a rest between litters).

If its her first litter and she's not too old, you can try to breed her in a month or two...and do your best to keep her in a stress free environment. It wouldn't hurt to have her checked out by a vet now, to make sure the still births aren't caused by internal or health issues.
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PHLdyPayne