Where to find Bellatrix's character stud in Harry Potter 5-7?

In "Harry Potter and the Order of the Phoenix," Bellatrix Lestrange's character study can be found in the context of her role as a loyal servant to Voldemort and her complex relationship with the Black family. She is prominently featured during the battle at the Ministry of Magic and is characterized by her sadistic tendencies and deep-seated hatred for Harry and his friends. In "Harry Potter and the Half-Blood Prince" and "Harry Potter and the Deathly Hallows," her character further develops as she becomes more involved in Voldemort's plans and reveals her fierce loyalty to him, showcasing her as a formidable antagonist. Her presence and motivations are explored through her interactions with other characters and her actions throughout these installments.