It could be Athena, as the spear and serpent are symbols of hers, but Athena doesn't actually do all that much in the Trojan War, as far as Achilles is concerned... my guess is actually his mother, which, by some accounts, would have been worshipped by seafarers, and would have been responsible for his invulnerabilityimmortality.
My guess would be Medea, Polyxena, or Briseis, but there aren't that many women in the various stories around Achilles that would've been around at his approximate time of death that would want to be reunited with him that he would be lashing out at... my hunch says the latter, as she implies he used to love her, and if her story arc didn't happen, Achilles' best friend (I think?) would've stayed alive, and a whole lot of the Trojan war would've been avoided.
But these few pages play so fast and loose with so many facets of the traditional versions and has enough internal inconsistencies that it really doesn't make too much sense... it's like the author wanted to do one of those ironic stories but couldn't come up with a situation on their own.