Is it permissible to strive to have my husband's brother divorce his second wife, and to access her email to uncover her true nature, and will Allah punish her for her actions?

Divorce is reprehensible in Islamic law and should not be resorted to unless reconciliation becomes impossible. No one is permitted to separate a husband and wife, as this is a grave sin and an act of sorcerers. The man should be advised to fear Allah and be made aware of the obligation to provide for his daughter. If he refuses, the matter should be referred to a judge. It is not permissible to say "he started disbelieving" without verification, but abandoning prayer is a serious matter that can amount to disbelief. It is not permissible to spy on a woman unless there is a clear necessity and obvious suspicion. No soul bears the burden of another, and the man is responsible for his actions, but the woman is sinful if she incites him to divorce his first wife and abandon his daughter.