It is very common, both cats and bitches, to be with milk after 2 months of calf. When the chicks are still with the mother, the first step is to start the separation by introducing the dry chow to the chicks. It is very common after breastfeeding the cat has mastitis, which also causes secretion in the breasts and redness with pain.
In your case, the puppies have already been donated, so it will be necessary to take more complex measures. There are medications to help milk dry, they interfere with lactation hormones, so they should not be used without consulting a veterinarian for an assessment of the real need to use the drug and differentiation with mastitis.