2 Corinthians 11:14 And no marvel; for Satan himself is transformed into an angel of light. 15 Therefore it is no great thing if his ministers also be transformed as the ministers of righteousness; whose end shall be according to their works.
If you believe it was Satan that appeared to the children at Fatima, I feel sorry for you.
Secondly, why would she tell everyone to pray the rosary everyday? Shouldn't she be leading them to her Son? Shouldn't she be giving them the gospel of the grace of God? We are told, in God's Word, to preach His word. To be ambassadors for Christ, to be reconciled to God by the finished work of Christ, that God made Christ to be sin for us, who knew no sin; that we might be made the righteousness of God in him. We are not ambassadors for Mary, nor are we given instructions by God to pray a rosary for ANYTHING.