She is engaged in this battle. The Blessed Virgin came to Fatima to give a warning and the remedy beforehand.
"In her 1957 interview with Father Fuentes, Sister Lucy spoke of a decisive battle between the Blessed Virgin and the devil. Though not as evident as the above-mentioned crisis of Faith and pastoral negligence, this third theme frequently appears in the communications of Sister Lucy. Yet what does she mean by "decisive battle"?
In her interview with Father Fuentes, Sister Lucy discusses this theme, saying:
“Father, the devil is in the mood for engaging in a decisive battle against the Blessed Virgin, and the devil knows what it is that most offends God, and which in a short space of time will gain for him the greatest number of souls. Thus the devil does everything to overcome souls consecrated to God, because in this way the devil will succeed in leaving the souls of the faithful abandoned by their leaders, thereby the more easily will he seize them.
“Father, the Most Holy Virgin did not tell me that we are in the last times of the world, but She made me understand this for three reasons. The first reason is because She told me that the devil is in the mood for engaging in a decisive battle against the Virgin. And a decisive battle is the final battle where one side will be victorious and the other side will suffer defeat. Hence from now on we must choose sides. Either we are for God or we are for the devil; there is no other possibility.
“The second reason is because She said to my cousins as well as to myself, that God is giving two last remedies to the world. They are the Holy Rosary and devotion to the Immaculate Heart of Mary. These are the last two remedies which signify that there will be no others.
“The third reason is because in the plans of Divine Providence, God always, before He is about to chastise the world, exhausts all other remedies. Now, when He sees that the world pays no attention whatsoever then, as we say in our imperfect manner of speaking, He offers us with a certain trepidation the last means of salvation, His Most Holy Mother. It is with a certain trepidation because if you despise and reject this ultimate means, we will not have any more forgiveness from Heaven, because we will have committed a sin which the Gospel calls the sin against the Holy Ghost. This sin consists of openly rejecting, with full knowledge and consent, the salvation which He offers. Let us remember that Jesus Christ is a very good Son and that He does not permit that we offend and despise His Most Holy Mother. We have recorded through many centuries of Church history the obvious testimony which demonstrates by the terrible chastisements which have befallen those who have attacked the honor of His Most Holy Mother, how Our Lord Jesus Christ has always defended the honor of His Mother.
“The two means for saving the world are prayer and sacrifice. [Regarding the Holy Rosary, Sister Lucy said:] Look, Father, the Most Holy Virgin, in these last times in which we live, has given a new efficacy to the recitation of the Rosary to such an extent that there is no problem, no matter how difficult it is, whether temporal or above all spiritual, in the personal life of each one of us, of our families, of the families of the world or of the religious communities, or even of the life of peoples and nations, that cannot be solved by the Rosary. There is no problem, I tell you, no matter how difficult it is, that we cannot resolve by the prayer of the Holy Rosary. With the Holy Rosary we will sanctify ourselves. We will console Our Lord and obtain the salvation of many souls.
“Finally, devotion to the Immaculate Heart of Mary, our Most Holy Mother, consists in considering Her as the seat of mercy, of goodness and of pardon, and as the sure door of entering Heaven.”
The following year Sister Lucy wrote again to Mother Martins:
"Thus the little pamphlets [referring to a text on the Rosary composed by Sister Lucy] will remain with souls, as an echo of Our Lady’s voice, to remind them of the insistence with which She recommended the prayer of the Rosary to us, so many times. It is because She already knew that there had to come these times, during which the devil and his supporters would fight so much against this prayer, to lead souls away from God. And without God, who shall be saved?! For this reason we must do everything in our power to lead souls back to God."
Finally, in a letter to Don Umberto Pasquale, who was very devoted to the cause of Fatima, Sister Lucy wrote:
"… The decadence which exists in the world is without any doubt the consequence of the lack of the spirit of prayer. Foreseeing this disorientation, the Blessed Virgin recommended recitation of the Rosary with such insistence. And since the Rosary is, after the holy Eucharistic liturgy, the prayer most apt for preserving faith in souls, the devil has unchained his struggles against it. Unfortunately, we see the disasters he has caused.
… We must defend souls against the errors which can make them stray from the good road. … We cannot and we must not stop ourselves, nor allow, as Our Lord says, the children of Darkness to be wiser than the children of Light … The Rosary is the most powerful weapon for defending ourselves on the field of battle.10
The theme repeated again and again in these letters is that we are in the last times and that the devil has therefore begun his last and most virulent battle for souls. And, as Sister Lucy explained to Father Fuentes, God has given us “the last means of salvation, His Holy Mother.” Therefore She is engaged in this battle. The Blessed Virgin came to Fatima to give a warning and the remedy beforehand."