When we write any essays or any literature stuffs and use a passive voice in the first sentence, do we have to write the whole thing in passive voice or active voice can also be used?

Millicent sat down at her desk in the big study hall. tomorrow she would come to school, proudly, laughingly, without lipstick, with her brown hair straight and shoulder length, and then everybody would know, even the boys would know, that she was one of the elect. teachers would smile , thinking perhaps: so now they've picked millicent arnold. i never would have guessed it. —"initiation," sylvia plath what inference can be made about millicent from the way she is characterized indirectly? millicent is a student with straight brown hair. millicent does not usually take care of her appearance. millicent has not always been popular.