This is just off the top of my head in about 5 seconds but could you say that Candy symbolizes the reality of the outcome of that life. As much as Lennie and George talk about making something out of themselves, it will always end with the same outcome. A cycle that can't be broken. Candy is everyone in a sense. The failure to live a prosperous and successful life.TBH the idea sounded good in my head ;D
I hope you understand the overall idea...