If an afterbirth is retained, it is the action of bacteria that helps it to break away. This is where the smell comes from. It is usually confined within the womb, so as long as the mother is well and eating, there's not a worry. The betamox lasts 48 hours so no need to repeat. It can take several days for the cleansing to come away, and as a vet, I know that if I try to pull it away before about 5 days after lambing or calving, it is more likely to tear, leaving some behind to cause problematic infections. As long as she is well, I would leave her until Friday, then if still hanging, you could get the vet out or pop her in to save the visit charges. Hope that helps