Ask the court to impute an income of at least minimum wage full time, more if she has an education or experience or past job such that she could reasonably make that higher income should she get a job in her field.
A judge will not let her get away with claiming an income of zero. Don't take your ex's advice on anything, go find answers on your own. Of course her lawyer is going to tell her things like this because it keeps the business flowing to him.