Blood in the milk generally would signify mastitis, but from what you say it doesn't sound like she has very acute mastitis. Acute mastitis would usually cause clots or little lumps in the milk as well as sometimes blood. It would be an idea to give the vet a call- as Pentre1230 says pencillin or cow tubes (which also have antibiotics in them) would work to clear up mastitis. Are you emptying out that side of her udder? Or are you just taking enough off to make her slack? If she's been kidded a month, and the kids aren't taking the milk that side, then you need to take off all the milk on that side.
Hope she improves!