One possible extreme revenge could be publicly embarrassing him. For example, she might expose his secrets or lies at an important social event where all his friends, family and colleagues are present. This would shatter his reputation.
She could also financially ruin him. If she has access to their joint accounts or information about his financial affairs, she might withdraw all the money and sell off valuable assets. This would leave him in a difficult economic situation. It could be a form of revenge especially if he has been unfaithful or treating her badly in terms of money management.