wild guess, probably will be proven soon, I say Olivia converted to the demon god since she came to know how the demon prisoners were resqued and considered it some divine intervention, so she thought "I'm gonna worship a god who actually gives a sh*t about their believers"
(if that's the case, do you guys think she was so affectious with Reinhardt knowing he was connected to the demons escaping? or maybe even knowing his true identity? i am jumping the gun here)