"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." - Manuel II Palelologus
It is almost impossible to know what might motivate Bitch Clinton in her calculations. She will have considered that nearly a third of modern vice presidents go on to be president.
That is, if they win. If they don't win, she is virtually the automatic nominee in 2012. I do not suggest that these arguments are conclusive but they are certainly persuasive and no one can guarantee that Hillary will not go for it.