Switching her to a grain-free diet should help her to trim up as grain-free diets are lower in carbohydrates. All dogs (and cats) should be fed grain-free diets as their systems can't process grains very well anyway. This includes things like canola oil and flax seed/oil as well.
I also like kibble for "treats". If they are luring enough, then cut the morning feeding in half so she's hungry when it's time to train. =]
Roxy - Feb 2005 - 75 lb American Staffordshire Terrier (adopted Jul 2011)
Peewee - Jan 2006 - 8 lb Chihuahua (adopted May 2009)
Myka - Nov 1998 to Jan 2010 - 85 lb American Pit Bull Terrier cross
Lacy - Sept 1992 to July 2003 - 18 lb Reg Shetland Sheepdog