The final scenes of the film reveal Brand’s whereabouts. She is on the surface of Edmunds, a planet orbiting the black hole in a safer trajectory than Mann’s planet or Miller’s planet.
The very last moment of the film connects Cooper to her. After Cooper is rescued from inside the black hole (the Tesseract) and wakes up on the Cooper Station space colony, he repairs the robot TARS. where was brand at the end of interstellar
However, Plan B—the "population bomb" of frozen embryos—is also in motion. While Cooper sacrifices himself to ensure TARS and Brand can escape the black hole (Gargantua), Brand is jettisoned toward the third potential planet, Edmunds. The final scenes of the film reveal Brand’s whereabouts
However, I think there might be some confusion with a character named Murph's teacher, Mrs. Brand. Towards the end of the film, Cooper does have a tesseract experience where he finds himself back in Murph's room at different points in time. After Cooper is rescued from inside the black
It is critical to note that Brand’s timeline is radically different from Cooper’s. While Cooper falls into Gargantua and is ejected near Saturn approximately 80 years later (Earth time), Brand experiences only a few hours or days of additional time due to the black hole’s gravity. Thus, at the very end of the film, she is effectively decades or centuries ahead of Cooper in relative time, but completely isolated.