If you can't get good grades in your education without tuning out everything fun in your life and cramming yourself to death, then you were never that smart to begin with.
You will have issues later on in your planned career when you didn't actually learn anything from your cramming study sessions.
Everyone has different skillsets. Some people can't balance shit to save their life, regardless of their inherent intelligence. Think of how many people were REALLY good at something but became obsessed with something unrelated and threw away their career.
And I hate to be semantic but "cramming" refers to studying at the last minute. There's nothing in the story so far that suggests she only waits till the day before to study. In fact one of the first gags/jokes in the story is the teacher asking her what she's been doing the whole week. She was studying the whole week my guy.