Our Lady of Fatima never requested that we should fast on bread and water on Wednesday and Fridays.
That particular request came from whoever is appearing at Medjugorje.
The old traditional fast days in honor of Our Lady were Wednesday and Saturday - it was a tradition attached to the Sabbatine Privlege.* I believe Ember Day fasts encompassed Wednesday, Friday and Saturday. The Irish consider a fast on bread and water a black fast. Matt Talbot used to fast like that. It's a good fast. Catherine Doherty fasted on bread and tea. Medieval mystics fasted on bread and beer - my preference. What? Anyway, fasts are good. Anyone can fast. Anyone can request you to fast. Fast whenever you like. St. Margaret of Cortona fasted on Sundays and feast days - despite the objections of her spiritual director. But I digress.
It's good to keep your apparition requests in order however. Better yet, heed the approved ones first - but only after heeding the teaching and discipline of the Church: keep the commandments, then sell what you have, and so on. Oh, and never put words in Our Lady's mouth.
*An indulgence attached to the Carmelite Scapular under these 3 conditions: 1) Chastity according to one's state of life; 2) wear the Scapular; 3) pray the Little Office of the Blessed Virgin or, if one could not read, fasting on Wednesdays and Fridays. Later, the rosary could be substituted for the Little Office.