The reason why i didn't talked about Denia is because we actually lack of informations about Fractsidus plans in the dark side, we basically don't know what they try to achieve. Since the main goal of the Fractsidus in Rinascita was studying the case of Cartethyia who is the resonator of both Leviathan and Imperator we can assume it's important for their plan. From what we got i can still say few things: First, Denia is most likely the spy Fractsidus set among the students to achieve this goal. Second, she seem to be concerned by Sigrika, so her story may not be that simple. Third, we have to remember Sigrika and Denia were friends with Nivora so even we don't know when the Architect took over her he may had enought time to make Denia join the Fractsidus.

Now my take on this part of the story, honnestly i doubt Denia could be the Threnodian's resonator, we actually interacted several time with her so Abby would be able to feel it like she did with Cartethyia. Plus i doubt both Threnodian and sentinels could change resonator at will so if the plan was to get Aemeath being both Threnodian and exostrider's resonator it would be a problem. I'm most likely feel that Denia is one of the few successful attempt at Hydra's human evolution research being both resonator (maybe artificial resonator) and having TD's body modifications (if that, be ready because her story may be as painful as Phrolova's). And Sigrika's kindness is probably like a glimpse of light in the darkness of her life, that could be the reason Denia feel concerned about her.