Great thread idea!
I think your last question - 'Why instead did she go back to "the heart of elvendom on earth"?' - speaks for itself. Arwen, it seems, longed for her people, & on some level surely she regretted the fact that she would not be reuinted with them, being sundered from the Rings of the World until the End. After all, she had been alive for thousands of years before meeting Aragorn, & though their love was undoubtedly strong, they were only married for 120 years, & 'together' only a little longer - a proverbial blink of the eye for one of the Firstborn.
After having lived for many hundreds of years under the assumption that she would spend countless more with her father & her people, it seems that Arwen's last days in Middle-earth, facing the finality of her decision, were tinged with doubt, grief, regret & longing.