Sovereigns and Six, the idea that Etrigani developed the Mark of Death is a truly awesome one, and it’d be amazing to employ in a campaign. In that regard I could see something of a paralleling between Etrigani and Illmarrow, where Etrigani is essentially what Illmarrow could’ve been had she lived. Admittedly it likely would not be a SIBERYS Mark of Death like Erandis had, but I think it’d be enough to tick Illmarrow off.
I always loved the idea of someone from a culture that hates Mabaran undead and who spent her entire life training to kill them falling in love with a Mabaran undead. In the “Kaius III is Kaius I but Kaius III” option, it’d probably be more of Kaius mentoring Etrigani in the ways of the Seekers than a romantic partnership, but still just as interesting, especially since he’d be her father-in-law. What sort of things might Etrigani be learning from the Seekers?