Eating an apple prevented her from suffering natural death, but it didn't prevent her from being killed by Aslan, and it didn't empower her to take on another form.
What you guys are doing is all kinds of crazy speculating that has absolutely no support in the texts. You're spinning ideas about what Lewis intended by the character, but you have nothing from the stories themselves to build on. The only scrap of hint Lewis puts in the text connecting the two is an offhand comment about "those Northern Witches" [note : plural]. That's it. Beyond that, zip, nada, nothing.
You can imagine a world where this kind of stuff goes on, but don't call it Narnia.