When dogs mate; what happens is they tie which could last up to 30 to 45 mins or less. You usually can not untie them because they are locked; but I don’t understand this because the baby is human. I am not sure if I understand this story at all. I would be wondering about the Mother. Sorry.... I just don’t know. I suppose this could happen.
Also, they don’t always last that long; but it would be very dangerous for someone to try and unlock them. They would usually be bitten big time and it could be really harmful to the dogs; in this case the dog and baby physically.
I feel the same way you do. If the mother is innocent, I feel horrible accusing her, but boy, this just doesn't seem very likely.
According to this page on dog mating, a large knot forms in the base of the penis, locking the animals together. Presumably, that mechanism was at work in this case.