"First of all, there are actually two different historical figures who have been chosen as inspiration for Snow White, the first is Margarete von Waldeck and the second is Maria Sophia Margaretha Catharina von Erthal. There is a nice short Mental Floss article about both:
'Margarete von Waldeck
Back in the mid 1500s, there was a beautiful girl named Margarete von Waldeck who lived in a mining town called (…wait for it…) Waldeck, a small community in northwestern Germany. Children worked in the mines there, so you can see where retelling of the tale eventually morphed the children into small men over the years. Possibly due to problems with her father’s new wife, Margarete moved out of Waldeck when she was about 17 years old, headed for Brussels. When she got there, her beauty attracted the attention of Philip II of Spain. Apparently someone didn’t care for the idea of Philip marrying Margarete, and she fell gravely ill. Most people thought she was poisoned, and her handwriting in her last will and testament was shaky enough to make most people think she had developed tremors, a sign of poisoning. This Snow White never got her prince – she died from the mysterious illness when she was just 21. To this day, no one knows who poisoned Margarete, but we can rule out one suspect: her stepmother was already dead.
Maria Sophia Margaretha Catharina von Erthal
Behind door number two, we have Maria Sophia Margaretha Catharina von Erthal, to be known as Maria from here on out. Born in 1729, Maria grew up in a castle in Lohr, Germany. The castle is a museum today, and if you visit, you’ll be able to look into a certain famous mirror. It’s believed that Maria’s father, Prince Philipp Christoph von Erthal, gave the looking glass to his second wife as a gift. Sounding a little familiar? Maria’s outlook under her stepmother wasn’t quite so bleak – there was no huntsman seeking internal organs for proof of Maria’s death – but scholars think it wasn’t an easy existence. “Presumably the hard reality of life for Maria Sophia under this woman was recast as a fairy story by the Brothers Grimm,” Dr. Karlheinz Bartels, a Snow White scholar, has said. Oh, and Maria’s story boasts “dwarves” in a fashion similar to Margarethe’s: it’s said that only smaller-statured men were able to fit in the nearby mine tunnels of Bieber.
And here's another more in depth article about Maria Sophia Margaretha Catharina von Erthal at Once upon a time, Snow White lived in Bavaria.'
Nice that they both have forms of Margaret for their names, right? So OUAT is safe either way although the name appears to be happy coincidence on the tv show's part.
But in the end, the chances of either of these women actually being the source story are very slim, especially due to dates and then the working of elements to fit the story. Not that there might not have been some influence either way--the tale could have influenced the historical accounts, too, after all--but in the end we have no concrete proof beyond coincidence of some elements--mostly the girls being of noble birth and having difficult family lives--combined with the hope for tourism dollars. That's the problem with history. It's really so nebulous.
But it is always dangerous to assign fairy tales to actual historical personages. Bluebeard is notorious for this and the proponents act as if only the nobility killed their wives in times past when they seek source stories and personages from Gilles de Rais to Henry VIII are offered up as the inspiration. Unfortunately, there have been wife killers throughout history. And there have been (step)mothers seeking to kill their (step)daughters throughout history, too. (Remember that the Grimms were notorious for making deadly mothers over into stepmothers out of devotion to their own mother, to oversimplify things.)" (Full Article)
While it is certainly plausible that there were historical origins for fairy tales that became fantastical through the game of telephone that is oral storytelling, it is equally possible that the prevalence of jealous stepmothers or wifekillers in the world created an easily applicable archetype. All abandoned children become Hansel and Gretel. All predatory men become the Big Bad Wolf. All girls who rise above their station in life to find marriage and happiness are Cinderella. This is why fairy tales are so deep within us. As Joseph Campbell says, "The latest incarnation of Oedipus, the continued romance of Beauty and the Beast, stand this afternoon on the corner of 42nd Street and Fifth Avenue, waiting for the traffic light to change."
Myths and fairy tales stick with us because they are about us.