Why does Fran Sullivan hire a private investigator in the novel, All Is Not Forgotten?

Fran knows Bob's ego is big and that he will cheat on her, so she hires a private investigator to follow Bob and document everything he does. She does not want any surprises when his campaign begins, including women who might say they were forced to be with him. She also wants the documentation in case he ever tries to leave her for one of his other women. In that case, she will use the documentation of his infidelity to gain more financially from a divorce.