Puppy Aggression

Question
I recently adopted a 12 week-old female GSD from an area rescue group.  Actually, from looking at pictures online, I think she is closer to 8 weeks old.  She had just been spayed before I got her.  The story I was told was that she and her litter mates were born to purebred GSD in a shelter.  The rescue group got them out.  The mother was adopted first, and they said she had a very sweet personality.  They weren't sure about the father, but from looking at the puppies, they think the father was a purebred GSD as well.  I agree with them.  We choose to adopt the calmest, sweetest female since we have an 18 month-old neutered male Maltese.  They seemed to get along fine in the beginning, but it has been a week now, and the puppy is over-powering the Maltese.  He spends most of his time hiding in the bedroom.  This afternoon I gave the puppy an edible bone.  When I approached her, she bared her teeth and growled at me.  She did the same to my two young granddaughters.  I grabbed her by the scruf of her neck, and told her NO!  Instead of crying or dropping the bone, she growled, and tried to bite me.  I was shocked since she has shown no signs of aggression in the week that we have had her.  I have put my hand in her feeding dish at mealtime to be sure she isn't food aggressive, and had no problem.  I have approached her when she has had other toys and treats in her possession, and again, no problem.  My husband gave her a similar bone when he got home from work, and she did the same to him. She bared her teeth and growled.  He repeatedly tried to get the bone from her and gave it back to her saying, "gentle, be nice".  I am now afraid that she may not be safe around my little dog, my granddaughters, and even myself.  I am considering returning her (even though I will not get a refund).  Could this aggression be due to early spay, separation anxiety, etc.  Why does she only do it with this particular treat?  It is an edible bone, and has roast beef in it.  Do you think this aggressive behavior will change?  Do you suggest that I consider returning her before someone gets hurt?

Thanks!

Sandie

Answer
''Elevation for small puppies:  Sit on the floor and gently put your hands around your pup's middle, below his front legs, and lift him up.  He is facing you.  Hold him for 15 seconds.  Repeat until he no longer struggles.  If he is past 10-12 weeks, lift his front feet off the ground, but don't pick him up.  

Cradling for small puppies:  Hold your puppy gently on his back, as you would cradle a small baby.  If he struggles, hold him firmly until he quiets for 10-15 seconds.  With larger pups, you can do this as your sit on the floor, with your pup between your legs.

Quiet lying down:  Place your pup on the floor on his side, with all 4 legs pointing away from you.  Use your hands on his neck/shoulder area and middle, to hold him in this position.  When he is quiet, praise him.  Lengthen the time that you keep him quietly in this position.  When he accepts this position well, handle his paws and muzzle, while keeping him quiet.''

The quotes mean this isn't my original work.  It is copied from my Puppy Raising Manual.  I have long used these or minor variations of them, and they are very effective.  You may want to give him a belly rub while he is on his back too.  Helps bonding.  There is a big difference between him rolling over and demanding a belly rub, and you choosing a time to roll him over and rub his belly.  The latter cements your place as pack leader.