My Bichon has started attacking from the rear as people walk by us. She is also starting to growl at people more and charge at them with angry barks. I rescued her from a puppy mill and have had her obedience trained. She did well there but lately has started this more agressive behavior. There has not been anything that has happened to her that should scare her. What should be my response when she growls and lunges towards people head on or from the rear?