My nine year old rescue Jack Russel who I have had eight years. She has been a fantastic companion and loves people and children. She is not yappy or snappy and loves to be with people. Last year she developed a complete melt down and goes into total anxiety and shakes with fear when she hears a gun shot even in the distance. The walk is over and she just jumps at me constantly. Has anyone come across this behavior and does anyone have any suggestion as to what I can do to relieve her stress ?