Why didn't the dogs fight the she wolf when she came into the pack to steal a fish during feeding time?

I think that you are talking about Chapter 2 part one. The she wolf that comes into the camp is actually a dog. Usually a wolf may come to lure a lone dog into a pack of wolves but this one seemed more comfertable in a camp of dogs and men as a wolf would, "I reckon you've called the turn, Bill. That wolf's a dog, an' it's eaten fish many's the time from the hand of man." The dogs recognise that it is a dog and do not attack.