Although Hermione Granger was a gifted student and a talented witch (not even Severus could disagree with that), she was not naturally gifted with magic. Perhaps it came from her muggle upbringing, not having other magical people in her life to model after, but her instincts were not strong. She studied voraciously, but not everything could be learned from books, least of all, the delicate art of mind magic. It was an innate thing, something that Snape had taught himself, not a thing to be researched and taught via blackboards. She showed no propensity for Divination or riding on brooms, both of which relied strongly on feeling and following instincts.