Wow. I really would love to see Lewis' response to this. No offense, but that statement is ignorant. Pure and simple. If you think that Aslan just "jumped on her and scared her", then you shouldn't claim to understand the books. Or even the films. Good heavens.
And uh...I hate to tell you this, but Tilda won't be back to play the Emerald Witch. Gresham has already said that they will cast someone else. Lewis wrote nothing nor said nothing to indicate that Jadis' spirit lived on in other beings. For one thing, Satan exists in many forms. He uses demons. He uses worldly things. His own "spirit", if you want to call it that, isn't a spirit. Lewis didn't make the White Witch a central character in any books but LWW and TMN. There was a reason. The White Witch's power came to an end in LWW. Lewis didn't envision her showing up elsewhere, and I think it would be nearly bordering on blasphemous to imply that Jadis and the Emerald Witch are the same being.
They come from the same line, they are NOT the same person, NOR are they the same entity. I can't even begin to say how much that post frankly, shocks and offends me. No offense to you as a person but...yeah. Oh, and if Tilda is cast as the Emerald Witch, you can be assured that TSC will be the very last Narnian film made for a long time.