One of the magic of fairy tales is, that they haven’t been protected by copyright laws, at least not those we know as classics today in their basic forms (it’s something different with the disney movies though, those are protected by copyright). Or no one cared some decades, centuries ago. They were told and retold, writen and rewriten, adapted, changed, embbeded into local and regional context, changed, mixed up, and again retold and writen down. Good luck with finding origins. 😉
You will find elements of Snow White in a number of tales and myths, or elements of other tales and myths in Snow White, and sometimes impossible to tell which of the tale copied the other. Just take Snow White and Sleeping Beauty – in both tales you have magically caused states of deathlike and long lasting sleep – and princes, heros coming along falling in love with the sleeping beautiful woman. Deathlike long lasting sleeps caused by magic is a rather common motif. Or take the beginning, which reminds of another Grimm fairy tale, The Juniper Tree, (there a woman wishes for a child as red as blood and as white as snow), and then there is the tale of The Glass Coffin, think I mentioned these two somewhere else already.
There is folklore classification known as Aarne-Thompson classification system (abbr. AT) and an updated version the Aarne-Thompson-Uther sytem (abbr. ATU). Snow White is classified there as 709, as is Gold-Tree and Silver-Tree and a couple of other tales. I found this text version of Snow White with links to compare with other versions and other tales of the same type. :geek:
Shakespeare wrote a piece, Cymbeline, in which a princess named Imogen falls into a deathlike sleep induced by a potion – her stepmother wants her out of the way, trying to kill her, but someone changes the potion into a sleeping potion. And there is a man from her father’s court the princess is in love with and marries secretly, name of that “prince” charming is Posthumus Leonatus (what a name). Posthumus has to leave court and land, doubts the faithfulness of Imogen, meanwhile Imogen’s father has to deal with war. There is a lot of drama happening before Imogen and Posthumus have their happy ending of course, true love and marriage blessed by the father. Go figure. That drama is from maybe 1611 (date is not certain, might be even older).
The Brothers Grimm noted the daughter of a high ranking state offical as their first source for the tale, Marie Hassenpflug. Her mother had Huguenot ancestry and so probably she heard or has read tales of Charles Perrault, a french writer known for Little Red Riding Hood and Cinderella. Hassenpflugs were well educated and not common folk, so can assume, they knew some classic tales from books. That the fairy tales of the Brothers Grimm are based on common German folk tales is a legend.
That doesen’t mean, that there haven’t been stories alike around before and for along time, folk tales, fairy tales, myths. Doesn’t rule out either, that people’s imagination was fired by real story like that of Margaret von Waldeck, mixed with already known myths or tales. Just look at how fiction is created today, writers very sure get inspired by other fiction, by myths, legends as much as real life stories. Guess wasn’t that much different in history. 
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