Why is there a delay in the response to a wife's prayers for the guidance of her husband, who regularly performs prayers, despite her continuous supplication and charity on his behalf?

The acceptance of supplication has conditions and impediments. It is not necessary for the supplicant to be given exactly what he asked for. Rather, it occurs in one of three ways, as stated in the noble hadith: either the supplication is hastened for him, or it is stored for him in the Hereafter, or an equivalent amount of evil is averted from him. It is advisable to continue supplicating and advising the husband, for guidance is in the hands of Allah.