Strange behavior

Question
My cocker spaniel has always been energetic and playful, but lately she hasnt been.  She just lays in the recliner all day and has just recently become very protective of a cat squeaker that i had gotten her.  I have a chihuahua also and they usually get along well, but now she just growls at him every time he tries to aproach.  Please let me know whats wrong with her and what can be done if anything

Answer
The first step with most behavior problems is a visit to the vet.  No amount of training will fix a physical problem.  

If the vet doesn't find anything, post a follow up question giving me details including her age, spayed?, obedience trained, etc.  

If she is a chewer, watch the squeaker toy.  If she starts to tear it up, discard immediately.  Same for any other toy.