Origin of the Snow White tale

"Snow White" is a German fairy tale known across much of Europe and is today one of the most famous fairy tales worldwide. The Brothers Grimm published it in 1812 in the first edition of their collection "Grimms' Fairy Tales". It was titled in (in modern orthography "Schneewittchen") and numbered as Tale 53. The Grimms completed their final revision of the story in 1854. It has generally been regarded as purely a tale of fiction; however, recent research suggests that the story may have been inspired from a real story.
Theories.
Folklorist Joseph Jacobs, in "Europa's Fairy Book", in his commentaries, points out that the story of Snow White seems to combine motifs from several tales.
Chione.
Scholar Graham Anderson compares the story of Snow White to the Roman legend of Chione, recorded in Ovid's "Metamorphoses". The name "Chione" means "Snow" in Greek and, in the story, she is described as the most beautiful woman in the land, so beautiful that the gods Apollo and Mercury both fell in love with her. Mercury put her to sleep with the touch of his caduceus and raped her in her sleep. Then Apollo, disguised as an old crone, approached her and raped her again. These affections led Chione to openly boast that she was more beautiful than the goddess Diana herself, resulting in Diana shooting her through the tongue with an arrow.
Margaretha von Waldeck.
In 1994, the German historian Eckhard Sander published "Schneewittchen: Märchen oder Wahrheit?" (Snow White: Fairy Tale or True Story?), claiming he had uncovered an account that may have inspired the story that first appeared in Grimm’s Fairy Tales. 
According to Sander, the character of Snow White was based on the life of Margaretha von Waldeck, daughter of Philip IV, Count of Waldeck-Wildungen (1493–1574) and his first wife, Margaret Cirksena (1500–1537), daughter of Edzard I, Count of East Frisia. According to Bad Wildungen city documents, she was famous for her beauty. Since 1539, she had a very strict stepmother, Katharina von Hatzfeld (1510–1546), and perhaps soon after, Margaretha was raised at nearby Weilburg at the court of Philip III, Count of Nassau-Weilburg. In 1545, she traveled through the Siebengebirge ("seven hills") to live with her mother's brother Johann Cirksena (1506-1572) at Valkenburg Castle, in present day Limburg, Netherlands. In 1549, her father sent her on to the Brussels court of Mary of Hungary, governor of the Habsburg Netherlands and sister of Charles V, Holy Roman Emperor. Margaretha's presence at the court was partially meant to improve the relationship of her father with the emperor and help the release of Philip I, Landgrave of Hesse, who had been imprisoned in Brussels for his role in the Schmalkaldic War. 
The situation at the court was complicated, as several high ranking personalities were striving for Margaretha, including Lamoral, Count of Egmont. Charles V's son, Crown Prince Philip, arrived at his aunt's court in 1549. Tradition has it that he pursued Margaretha during the few months he was there, as well, though no official relationship could occur, as she was Lutheran. Three surviving letters from Margaretha to her father show that her health declined steadily over the next few years and she died at the age of 21 in March 1554. In Waldeck chronicles, she was suggested to have been poisoned. Since, however, her father's second wife died in 1546 and he only remarried again in October 1554, her stepmother never was a suspect in the alleged poisoning case. 
Margaretha's father owned several copper mines; a majority of workers were children, and Sander suggested that the legendary reference to the seven dwarfs is related to child labor in the mine. The residence of the seven dwarfs has been suggested to be the former copper-mining village Bergfreiheit, now a district of Bad Wildungen that calls itself "Schneewittchendorf" (Snow White village). Like the fairy tale's dwarfs, the child laborers there used to live in groups of about 20 in a single room house.
Maria Sophia von Erthal.
According to a study group in Lohr, Bavaria, Snow White is based on Maria Sophia von Erthal, born on 15 June 1729 in Lohr am Main, Bavaria. She was the daughter of 18th-century landowner, Prince Philipp Christoph von Erthal and his wife, Baroness von Bettendorff.
After the death of the Baroness, Prince Philipp went on to marry Claudia Elisabeth Maria von Venningen, Countess of Reichenstein, who was said to dislike her stepchildren. The castle where they lived, now a museum, was home to a mirror that was famous for its extremely smooth and even surface, something uncommon in that period. It was referred to as ‘talking mirror’, because “it always spoke the truth” (now housed in the Spessart Museum). The mirror, constructed in 1720 by the Mirror Manufacture of the Electorate of Mainz in Lohr, had been in the house during the time that Maria’s stepmother lived there. Her gravestone was found in 2019.
The dwarfs in Maria’s story are also linked to a mining town, Bieber, located just west of Lohr and set among seven mountains. The smallest tunnels could only be accessed by very short miners, who often wore bright hoods, as the dwarfs have frequently been depicted over the years.
The Lohr study group maintains that the glass coffin may be linked to the region’s famous glassworks, while the poisoned apple may be associated with the deadly nightshade poison that grows in abundance in Lohr.