Nona was just a shard of Alecto’s soul that came out when Harrow kissed her all those years ago. The full Alecto (aka whatever of Earth’s soul remains after Jod took a bit and put the leftovers in a barbie) is what woke up at the end but harrow.

At birth Harrow had her own soul only (or possibly shrapnel from the child murder that lead to her conception but that seems increasingly unlikely).

At a young age Harrow unlocked the tomb with Gideon’s blood on her fingers. When she kissed Alecto’s frozen corpse she got a little bit of Alecto’s soul stuck in her somehow. Necromancy. BTW, at a similar time commander wake me up in side’s soul ended up in Gideon’s great sword.

After lictoring Gideon Harrow had her soul too and only digested some of it before she lobotomized herself. BTW around this time Commander wake’s soul leaves the great sword and takes over the body of the dead lictor.

At some point near the end of HtN Gideon’s soul takes over harrow’s body and harrow’s soul locks itself away to let Gideon have a turn driving. This lasts about 10min before Gideon gets her ass beaten and her soul comes out in the river. BTW this is where Jod gets her soul for making the tower prince with.

With no one else left in the body the shard of Alecto called Nona takes over. At the end of NtN the shard is reunited with Alecto and Harrow takes back over her own body. For the first time since before GtN everyone’s soul is where it should be except for the part of Gideon’s that harrow ate to become a half lictor.

It is not exactly clear how alecto work up (I personally blame Paul but idk) or how harrow’s soul took back over, but these aren’t huge mysteries.

Hope this helps. Not spoiler Ed because that is what this whole thread is.