Rachael (Sean Young)’s Timeline and Summary

Rachael starts out as a replicant who doesn't know she's a replicant—an experiment, kept by Dr. Eldon Tyrell.
When Rick Deckard shows up, he administers the Voight-Kampff test to her, and discovers that she's a replicant—though a special one, very difficult to detect and with false implanted memories.
Later, at Deckard's apartment, he reveals to Rachael that she's a replicant.
Rachael goes on the run, and the blade runners are instructed to kill her.
But Rachael manages to save Deckard's life, shooting another replicant, Leon, as he tries to kill Deckard.
Back at Deckard's apartment, Deckard and Rachael sleep together.
After Deckard has concluded his final confrontation with Roy Batty, he rushes back to his own apartment, discovering that Rachael is still alive and that Gaff spared her life.
Together, Deckard and Rachael lead the apartment, ready to start a new life together.
In the theatrical-release ending to the film, it's revealed that Rachael doesn't have the four-year lifespan limit that the other replicants have. She and Deckard are apparently going to live in a beautiful natural setting, far different from L.A.