Para dizer "estudioso" ou "estudiosa" em inglês, sugiro "studious
(adj.) = very inclined toward the mental activity of learning, reviewing, and mastering subjects of knowledge, perhaps also combined with the goal of getting good grades if still in school or university. (wordreference
Exemplos de uso:
- Ela é estudiosa. Só tira notas boas.
- She is studious. She gets only good grades.
- Ele é estudioso. É o melhor aluno da turma.
- He is studious. He is the best student in the class.