abused peke puppy

Question
I got a female pekingese a week ago from a pet shop that assured me she came from a wonderful, loving breeder. However she doesn't act like a normal 4 month old puppy and I feel she was abused before I got her. It took her several days before she stopped flinching every time I put my hand towards her. She's become very comfortable with me, we play together and she constantly comes to me to have her belly rubbed. She is very happy and affectionate, but when she is around anyone else she cowers, puts her tail down and hides behind me. She also has a fear of being picked up, she'll run away and then get very stiff when I hold her.

I know she has to be socialized but I don't want to traumatize her into never being good around people. I've taken her to a park to people watch and also had a friend come over to sit and give her treats so she would associate strangers with getting good treats but she would just grab the treat and run back to me, then refuse to go over to them when the treats were gone.

I also don't know how to discipline her about her constant habbit of chewing on everything (including electrical wires.) I've tried telling her no, distracting her with a noise like clapping or with a toy but she immediatly goes back to chewing. I know I have to be the pack leader, but because of her previous abuse I feel like I have to be extremly gentle with her so I don't lose her trust.

This is my first dog and I don't know what to do.

Answer
All pet store puppies come from puppy mills or backyard breeders, and are often un-socialized during critical stages of development (age 8-12 weeks).  You should RUN, don't walk, to the nearest positive trainer in your area and enroll in puppy class, so that your dog can have safe contact with other dogs and people.  As to the chewing, she cannot be left unsupervised at this age.  I doubt very strongly that this puppy was ever abused.  It sounds like she is a mill pup that simply never had the appropriate experiences that reputable breeders provide for puppies.  Sorry, I just need to be honest with you - the store likely lied.  Their "breeders" are usually USDA volume breeders brought in from large suppliers like Hunte (Google that).