biting cocker spaniel

Question
We have a 2 yr old female cocker spaniel.  She has never shown any aggression or biting until recently.  This happens when we are in our pickup and an individual comes to the window.  First it was a man helping me to enter coins into a car wash.  Then another man was talking to us and touched the pickup and she started snapping.  Then today our daughter was talking to us.   She knows the dog so she is no stranger.  This has happened three times and must be curbed.  She is possessive of our pickup.  We have three vehicles but feels possessive of the blue pickup.  We are an older couple and the three of us are very close.  The first incident I was along with the dog.  The other two times we three were in the pick up.  Help!  Thanks  

Answer
First, you need to control your emotions.  Spay her is not already.  It is no cure all, but reduces many problem behaviors.  Greet people that approach as warmly as is appropriate.  Try having people give her treats.  Doesn't need to be elaborate.  Some if her regular kibble will be fine unless she frequently gets other treats.  

Otherwise, it could only get worse as she nears maturity at 3 years old.  if the above doesn't work, you may need to try a professional trainer or dog behaviorist.