Maybe.
I had thought she was a ghost -- she and Onni seemed to agree that she's dead. But maybe Onni thinks the human part of the people who turned into trolls are dead? -- just read through the section again, and while Onni does seem sure that she's dead and she at first agrees, a few pages later she says she thinks she died but she can't really remember. (page 568, and then 571)
If that is her: I wonder how in control she is.
But if that is her, and she can help the ghosts finish dying and then let herself do so: can she also free into death the (other) people caught in trolls?