Your point is well taken and I should have stated some chickens and not all chickens, after all, I have some that are more aggressive than others and some you can not break the habit because of their breeding, such as some locally hatched chicks I have, I had to cull 4 roosters that were overly aggressive towards each other and my hens, One of 5 were none aggressive and he is the soul flock leader although I have other breeds, they have their own flock and are somewhat aggressive, I also had some Black Australorps that never fit in to the flock, they caused havoc 24/7,the were not aggressive to humans but they were pure torment to the flock, I gave them time and worked with them for many months, I finally harvested them, what a difference, within 3 days ,egg production nearly doubled, I may try them later on because I love the breed, but they wont be hatchery chicks next time. I have some that are always in my face for attention, they squat anytime I get near them and some approach me and squat and if I don't pick them up and move on, they will run and get in front of me and squat, repeating this till I pick them up.... 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.