"How can it not know what it is?"
The most important thing about Rachael is not her gender, nor her actions (even saving Deckard). Her identity is one of the central cruxes of the story. She is a replicant that has been "gifted with a past". She is a human in all but fact, and as she and Deckard fall in love we watch her "human" status circulate: human , replicant (after test/confrontation), human (saving Deckard/falling in love), replicant (target by Gaff?), human (lover to be saved from harm).
Like Deckard (like all of us), Rachael has a constructed identity. Her sense of "self" is violated at the basic level when Deckard confronts her and recounts (recalls, for her memories became his) her memories to her. Cracks in the foundation can cause a building to fall. To re-present herself, Rachael must re-vive (vivre: Fr, to live) her humanity using new forms, new foundations.