Young puppies are almost never attacked and hurt by older dogs. When a puppy gets older, however, he loses that special aura of protection and is more likely to be thrashed for misbehaving.
The age at which a puppy has to act like an adult varies. In a multiple dog household, the older animals will start training the young dog as soon as he gets home.
It is hard to tell what the dynamics are between your older dog and your puppy, but it sounds like the puppy is becoming an adult and is being seen as challenging. Of course, some old dogs never like the new puppy trodding on their home turf, and will attack without provocation.
What kind of training have you done? Are you in charge? You need to spend some time in the backyard with them when you let them out. Watch the older dog, and see if the puppy is committing some "crime" that is causing the attack (stealing favorite toys, for example). If this is the case, you can remove the triggers, and the dogs might get along.
If the dogs still fight, you should try to talk to a behaviorist, and you may even need to rehome the puppy. It is not right to make her grow up and live in a world where she is always afraid of being attacked.