That title would certainly fit, though we never got any casting calls or info for the character Lady of the Lake, which is curious. Hmmmmm.
http://en.wikipedia.org/wiki/Lady_of_the_Lake
The Lady of the Lake is the name of several related characters who play parts in the Arthurian legend. These characters’ roles include giving King Arthur his sword Excalibur, enchanting Merlin, and raising Lancelot after the death of his father.
More about Lancelot’s connection to Lady of the Lake is here:
http://www.timelessmyths.com/arthurian/lancelot.html#Lady
This couldn’t somehow work into the “complicated relationship” Lancelot has with Snow, could it? Lady of the Lake couldn’t have been Snow’s mother, could she? And when she was given the task to save baby Lancelot, she had to choose between that or staying with her daughter, and she chose the former? Has it been specifically said Snow’s mother died, or is she just ambiguously “lost”?