She hasn’t. Take a look at the last page of Unveiling for instance. Eris considers the Darkness to be wholly evil. She considers that even if the world was balanced between Light and Dark that the world must fight the Dark, for if it is unchecked it shall only thrive. She also despises the Dredgens despite her own dabbling with Hive magic. Eris seeks to eradicate the Hive from existence and has now also come into contact with the God her foe serves. That smile Eris lets off in the cutscene tells me that this one lone Pyramid may be underestimating her abilities as a Lightless and thusly we may actually be able to use her research against the Pyramid Fleet when it arrives.