... I think you've mistaken me for the OP.
I don't have aggressive chickens, I culled them out ages ago; it's amazing how heritable it is.
I understand it's true for you, but I disagree with the line of yours I put in bold: it's only true for
some chickens.
Not all chickens are aggressive, and those that aren't don't give a fig what color shoes you're wearing or whether or not you're wearing shiny things.
Cannibalism, feather picking, bullying, pica, excessive noisiness, these are all heritable traits that not all chickens have, and you can breed it out of (or into) any given line of chooks. They are not traits inherent to the species, they're artificially introduced under bad husbandry methods maintained for sufficient generations.
The fact that this hen was showing trust and affection to begin with and jumping up to peck are a few major signs it's not a simple dominance issue, though she also sounds like she's aggressive.
Anyway, to the OP: you don't believe it's pica whereas I do, this much is obvious; I accept your belief on this even though I believe differently.
If the rescue place is any good they will take back the hen, since she now needs rescuing again. If you choose to cull her instead, hope that goes smoothly for you and her, and hope you don't beat yourself up about it too much, sometimes it's the best thing to do.
Best wishes.