Well, it's a nice thought but not all that viable in conjunction with where my theory goes. The prophecy only speaks of "him." And what iIm pointing out in my theory is that the "Dark Lord marked him as his equal" [the one that has the power to kill him] (italics mine). Lily wasn't a Death Eater and unless we're being left out of a wicked secret, Lily isn't a man either. Besides, Voldemort didn't die at Lily's hand. He was vaporized by her magic by proxy. She may have set in motion the chain of events that lead to his actual demise but it wasn't/won't (impossible at this point since she's dead) be by her hand.