I actually just posted about the Blood Libel over in Post a Day...
My understanding is that the idea that Jews were consuming Christian children's blood was not quite a thing in Mythic Europe. It would become part of the blood libel legend in 1475ish. But you could port the idea back to 1220. (Or I may be wrong about dates!)
Obviously taking the idea that Jews are actually consuming Christian blood as a real thing that happened in Mythic Europe would be setting your troupe up for a deeply antisemitic story. I do not recommend 
But you could use the story to deal with Christian anxiety around cannibalism, and the crimes they commit in the name of preventing it.