I was stupid enough not to spay my first Golden, not because I wanted to breed her or couldn't pay the bill, but because I thought it would be painful for her. She died of breast cancer at the age of 9 1/2. That was a long time ago and I learned my lesson.
My next two Golden girls were spayed as soon as they were six months old. They never gained weight or had any incontinence problems.
Please, do your pup a favor that will keep her with you, happy and healthy, for a long time. Spay her!