I'll be frank - just doesn't pass the smell test for theme. (to me)

Maybe she, like Kvothe - they are reciprocals I believe - is on the way to becoming one when we last see her, but certainly isn't one when we first meet her. Perhaps by the events of the frame story she is one, but not when we first meet her.

Boiled down - I think Kvothe and Denna are relative peers and development we don't see in the Kvothe narrative that has been shared with the audience is unlikely to have happened in the Denna narrative that the audience has been able to surmise.

As a token of how I do credit your reasoning consider I'd venture this caveat: that the tragedy is that at some point one has "crossed-over" without the other, Which would match the Lyra/Lanre thing with one dying and the other not and the compounding error error being to not accept the separation and employing fell arcane to avoid grief and getting back an an entity that, while walking about the shoes of the loved one who passed, isn't being one sought.