Why has she changed??

Does anyone know why a dog would randomly just start acting different and not listening and being a total menace?? She is over a year and is not going through heat yet. She just all of a sudden refuses to obey and breaks and destroys everything! You can't punish her, nothing works. She just keeps at it! She doesn't respond to positive training, I'm at the end of my rope. I don't know if I can handle her anymore. She use to be so good! Very well behaved and listened great. She just all of a sudden swapped.