shit-zu becoming cross

Question
How can I get my female shit-zu to be friendly.  She is afraid of all people except family.  Now she is starting to snap at them.  Before she only growled.  Usually when I pick her up she allows them to pet her but today she actually tried to bite someone who went to pet her while I was holding her. We have had her since she was a wee puppy and she was never mistreated but came from a very quiet private home where they worked all day and only the puppies were home. She never saw many people and now it is usually just me and my husband because we are retired.  The family does come and we go to visit.  She is okay with them.

Answer
This is typical of puppies that didn't see many people before they were 12 weeks old.  It can even be more difficult if it didn't include little kids.  You need to do 3 different things.  Have people give her treats.  It may be better to give them to them ahead of time.  Treats don't need to be large or rich.  Some of his regular kibble will do.  

You also need to give him better leadership.  You need to be in control and attend to biting people as needed.  If you are top dog, then he doesn't need to.  The key to most behavior problems is approaching things using the dog's natural instincts.  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/  For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm

The third thing is to remain calm and positive when people come.  Make sure he can see you are glad to see them.  Stress out over him, and he will see the people as being the problem.