Someone here, I can't find it now, had a theory about Ruby. I took the liberty of expanding this theory a bit and making it solid for the entire plot. This is what I came up with. And I'd like to hear your thoughts.
- 30 years ago, Ruby arrives to the cabin and finds her dead Deadite mother and Annie, still with the Kandarian dagger (held by Ash's hand) in her back. She collects the dagger and the hand, but she can't find the Necronomicon (because Ash has it, FOR SOME REASON).
- In the following years, Ruby studies the ancient forces of Evil and she is finally able to contact one of the Dark Ones. The Dark One wants the Necronomicon, but the Evil can't yet enter our World (not until the first episode where Ash summons it by accident), so the Dark One makes a deal with Ruby.
- He tells her that Ash killed her family and stole the Necronomicon, and that if she finds Ash and gives the Necronomicon to him, he will bring the Knowby family back to life (or at least Ruby's father, who's maybe not yet dead, but rather still imprisoned between two worlds, as was stated in Evil Dead II).
- Ruby agrees, but she knows that she can't trust the Dark One and therefore she secretly want's the Necronomicon for herself, so that she could use its power to save her family on her own.
- After Ash summons the Evil and Ruby starts killing off Deadites (Kelly's dad, Lionel), the Dark One realises that Ruby has no intention of honouring their agreement. So when Ruby meets Brujo, he "Drags her to Hell", where the Dark One possess Ruby's body, so that he could get the Book himself. The only question that remains is whether Ruby is now dead/in hell, or she is still there somewhere and can fight the Dark One.
The only thing that doesn't make sense is why it took Ruby so long to find Ash. As someone stated before, he never left Michigan and was just going from one Value Stop to another and Ruby was actually able to find him only after the hand woke up. But I don't think the show will explain this. It's just one of the plot holes I think we all can live with.