Why couldn't Celty find what she was looking for?

Question

In the anime,

What kept Celty from getting her head back?

Out of everything in this particular anime, this is the only thing I still don't grasp.

Can anyone shed some light on this for me?

Answer 1

According to the Durarara Wikia page for Celty:

In Volume 4:

As Celty reflects on her life since coming to Japan, she realizes that she doesn't mind things staying the way they are with or without her head. She has friends who accept her, a stable job as a courier and a lover waiting for her at home.

I can't remember how overt this was in the anime but

When it's revealed that Mika Harima doesn't actually have Celty's head, Celty never really has a chance to search for it. It's left completely unresolved at the end.