Go to Canadian Immigration site. I am sure there is something for student dependent visa.. If not.. then i dont think u need to do anything until the authority calls you for the verification.  Legally she is no one to you... as a relative so even if she commits any crime, you cannot be held responsible.

BUT

When Authority calls you then tell them the truth.

When you  marry in nepal and applying for your new wife's visa.. tell them that the ex wife visa needs to be revoked .