It's normal for you to feel a little jealous. She's going to want to be part of your puppy's life, and that's good, because dogs are part of our families, not possessions of one person. I strongly disagree with the person who said that only one person should train the dog. As a professional dog trainer, I highly recommend that training be a part of the family as well, because a well-trained dog must listen to everybody in the household.
Ask your parents to help you with your sister. Tell them what you told us. It's very likely that she'll be really excited at first, but then after the novelty wears off and the puppy starts chewing up her stuff, and she's on the receiving end of puppy biting, she'll be calling you to come get YOUR dog!
I highly recommend getting into a puppy socialization and training class ASAP. Aussies are great dogs, but they need socialization and training to be great dogs. Because they are herding dogs, they will chase anything that runs, and 6 yo girls tend to run and jump and squeal, so you're likely to run into problems with that behavior. They also can be dog-aggressive as adults if not well-socialized now and through the first year , so getting the puppy out to play with other friendly, vaccinated, healthy dogs is very important.
Call a trainer from the Association of Pet Dog Trainers:
http://www.APDT.com
Tell your parents that you want to crate train the puppy, and keep the crate in your room at night. Make sure that your little sister understands to let the puppy rest when she's tired, and not to hold and squeeze the puppy until it bites to get away from her. Make sure that nobody play tug games or plays "handsy" games with the puppy-- those all will encourage puppy biting, and you'll want to teach the puppy to put his mouth on toys instead.