Does a wife's informing her mother of her husband's religious secret, out of fear of death during Hajj, constitute a disclosure of a secret that necessitates repentance, knowing that the husband is angry about it?

You erred by disclosing your husband's secret, which he entrusted to you and ordered you to keep confidential. Informing your mother does not absolve you of this mistake. Disclosing secrets is prohibited, especially if the owner of the secret has commanded its concealment, and it may be Haram (forbidden). You must ask your husband for forgiveness and not repeat such an act.