Section 7 of the Hindu Adoptions and Maintenance Act, 1956 makes the wife's consent mandatory for a married Hindu male's adoption, subject to three specific exceptions written into its proviso. Each option can be checked against those three exceptions.
Checking each situation against the three statutory exceptions shows that only conversion out of the Hindu religion removes the need for the wife's consent among the choices given.
Therefore, the correct answer is She has ceased to be a Hindu by conversion.