She lets her go outside sometimes, out onto the surface.
No, “let” isn’t the right word. Let implies the sort of authority that she no longer holds over the human woman, the power that once allowed her to control her favorite plaything and lead her through whatever literal hoops she pleased -
except, no, she never really had that power either.
Chell had trampled her way through anything and everything thrown at her, exactly the way she wanted with a flippant disregard for protocol - the constants of this place that had been set for the both of them. Rules of their world that were placed upon them long before either had woken to unfamiliar ceilings for the first time.
She isn’t as afraid to admit that she has no control over anything, anymore. At least not where her lunatic is involved.
It’s funny how things change, with a little time and a few mutual attempts at murder in the equation.
Chell goes outside sometimes, out onto the surface. She would spend hours, sometimes a day out in the endless field of rustling stalks. She would come back smelling of the equally endless sky, trailing dirt and leaves and sometimes drops of dew over the immaculate white tiles.
GLaDOS stays inside.