The origins of the name of La Morenita are still relatively controversial.
Guadalupe, strange as it may seem, is most likely not a Mexican name. In fact, it is not even Spanish, although it is originally the name of a river in the Spanish province of Extremadura.
According to some, Guadalupe is a Castlian, or standard Spanish version, of the Arabic Wadi-al-lubben, meaning “the hidden river.” The Arabic is no surprise: one must keep in mind the Iberian Peninsula was occupied for around eight centuries by the Moors, Arabic-speaking Muslims from Northern Africa. According to others, the name is an Andalusian mixture of Latin and Arabic (known as, precisely,“Latin Arabic”), Wadi-lupe, “the wolves’ river.”
Before the miraculous appearance to St. Juan Diego in Mexico, Our Lady of Guadalupe was already a figure of veneration among Spaniards. According to legend, a miraculous statue of Mary with dark skin — a so-called “Black Madonna,” one of three venerated around the world and said to have been fashioned by St. Luke — was buried near the Guadalupe River when the Moors conquered the area. Early in the 14th century, a shepherd claimed that Mary appeared to him and told him to dig at the spot where the image was buried. The image was enshrined and became a center of pilgrimage and an inspiration in the Christian Reconquest of Spain. That first image is more commonly known today as Our Lady of Extremadura, for the region of Spain where the image was uncovered.
So it is certainly possible that if the name La Morenita gave to Juan Diego was Guadalupe, the Spanish bishop would recognize and honor the title.
But there is also the possibility that the name Guadalupe originated from Nahuatl, the language spoken by some of the natives of Mexico. Juan Diego spoke Nahuatl as well as some Spanish, and in the accounts of the apparitions Mary also spoke to him in Nahuatl. Some have suggested that Juan Diego called the Lady Coatlaxopeuh, Nahuatl for “she who defeats the serpent.” Or perhaps he said Tequatlanopeuh, “she who is on the rocky summit” (referring to the hill of Tepeyac, where Mary first appeared to Juan Diego). In either case, the bishop might have “heard” the phonetic pronunciation of these names as the already-familiar Guadalupe.
As interesting as these theories might be — Christianity did in fact, with the Lady’s help, defeat Quetzalcoatl, the “feathered serpent” representing pre-Christian cults — there is no contemporaneous evidence that these names were ever used to refer to Mary. Instead, manuscripts and chronicles of this early colonial period relate that the Mexican people insisted in addressing the Virgin as Guadalupe from the very first day.