Chocolate labrador behavior

Question
We adopted a 8 years old chocolate labrador at Humane Society that belonged to a elderly couple currently unable to care of her. Our intention was bring her to be companion to Pete, a rescued dog that had Tasha for all his life. And Tasha was killed.
Gretchen, our lady labrador, behaves like a puppy and we give Pete a hard time because she used to be the center of attentions and now has to share with him.
She is jelousy and uses her big body between us and Pete everytime we want to love him.
Both have our love and attention.
Besides her habit to chew and destroy, she faces difficulties about share attention, be an outside dog instead a inside on her past.
They have insulated houses, blankets, water and special food; I mean, we do our best.
But I just don't know how to do to teach her comands or what teach, improve her behavior and see her not anxious like she seems to be. She breaths deep, she doesn't stop and I wonder if she is ok, if we are not doing right.

Answer
You need to talk to a vet about the breathing and find out if it has a physical cause.  

Start her in an obedience program, either working out of a book or a class. The dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog.  Life is much easier if the 2 legged pack members outrank the 4 legged ones.  You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/