I assume if she was a teller and saw, say $100MM, in an account assigned to him, it wouldn't be unimaginable for her to believe whatever story he conjures up.
Also he paid her half a million (a million in today's money) for her help. Less a wife, and more a special kind of legally protected employee.
Charles Manson married one of the witnesses against him in order to prevent her from being compelled to testify.