Before Moro attacks the humans for "defiling the forest", they had found her puppies and killed one of them. Then the humans sacrifice their baby so they can escape. (Whether they actually escape or not is unclear.) So Moro decides to raise San as her own to replace the pup that she lost. The pelt is from the dead puppy so San could stay warm. * The ears and mask put on it were so that San could hid her human features which she detested. She grew up with a warped sense of beauty, never considering herself to be so. This is why it shocked her so much when Ashitaka said that she was beautiful.