Loose stools are common after calving. That said, it can be simply part of the process, or parasites taking advantage of the process. Between the fluids on the baby, the hormones, and often, new diet, things can get crazy in their gut and loose stools can be normal. But it is also common to get coccidia or other worm "bloom". Did you treat her prior to the birth for intestinal parasites? If so, and she is having no other issues I would wait and watch. Otherwise I would have a fecal analysis done and treat accordingly. Especially since you don't want the baby to get coccidia.