Behavioral theorists purport that anxiety is a learned behavior. From her past history, it seems that some of her behaviors could have been learned. We know that, as a child, she was removed from her mother and placed in foster care at the age of 2. Retreating to quiet places and hiding may have been reinforced behaviors from an early age. One would also wonder how she responded to the new environment and how her anxiety was relieved at that time.
Psychoanalysts believe that anxiety is expressed based on early mother child experiences.
Regression to an earlier stage of development often occurs.