Why can't I find Eileen in Bloodborne?

I'm curious, why exactly can't I seem to locate Eileen, the Crow Hunter, in my playthrough of Bloodborne? I've been searching high and low, checking all the usual spots and triggers, but she just doesn't seem to be appearing. Is there a specific questline or sequence of events that I need to complete first? Or is there a certain time frame or area that I've missed? I'm really interested in engaging with her story and abilities, so any insight you can provide would be greatly appreciated.