The name Magdalen comes from the word migdol, which signifies "watch-tower", whence the name of the Decapolitan city Magdala, and of the Abyssinian Acropolis; but obviously in Europe it has been given in memory of the touching Bible narrative, or on account of its musical sound.
     Its popularity was afterwards increased by the admiration felt in Roman Catholic countries for St. Mary Magdalen of Pzzi, who was born in Florence in 1566 and who was of noble parentage.
     Catherine, not Mary, Magdalen had been the name given her at her birth, but she changed it to Mary Magdalen when she took the vows of the Carmelite Order, and entered the monastery of St. Fridian, near Florence, at the age of fifteen. (Girls' Christian Names, Swan, 1905)

... Even the earliest writers of the Gospels were at a loss whether to identify the meek contemplative Mary of Bethany, by the woman that was a sinner, who is recorded as performing the same act of devotion, and with Mary Magdalen, once possessed by seven devils and afterwards first witness of the Resurrection.  While inquiry was cautious, legend was bold, and threw the three into one without the slightest doubt, going on undoubtingly to narrate the vain and sinful career of Mary Magdalen, describing her luxury, her robes, and in especial her embroidered gloves and flowing hair, and all the efforts of Martha to convert her, until her final repentance.  The story proceeded to relate how the whole family set out on a mission to Provence, where Martha, by holding up the cross, demolished a terrific dragon; and Mary, after having aided in converting the country, retired to a frightful desert with a skull for her only companion. 
     The word itself is believed to be a mere adjective of place, meaning that she came from Magdala, which, in its turn, means a tower or castle, and is represented by the little village of Mejdel, on the lake of Tiberias, so that her proper designation would be Mary of Magdala, i.e. of the tower, probably to distinguish her from Mary of Bethany with whom she is confounded. (History of Christian Names, Yonge, 1884)