What is the Harry Potter movie in which lady takes over Hogwarts?

You're likely thinking of Harry Potter and the Order of the Phoenix, where Dolores Umbridge, the new Defence Against the Dark Arts teacher, takes over Hogwarts as the Minister of Magic's representative.

She implements oppressive rules, establishes an Inquisitorial Squad to spy on students, and restricts any teaching of real Defence Against the Dark Arts, effectively suppressing students' learning and Hogwarts' free spirit.