Help! Dog with severe separation anxiety!?

My dog has severe separation anxiety when my mother or I am not home. I am going to college and she becomes especially depressed and her anxiety is worse when I am not around. We are hoping to cure her before I leave in August, or at least make a huge improvement. When we are not home she eat the curtains and furniture, urinates and defecates, whines barks and cries, runs wild around the house, and makes a mess of the garbage and pantry. Additionally, when I am not home she becomes extremely depressed. She sits outside my door crying, won't play with her toys and is all around mopey. Does anyone have any advice? Will getting another dog help?