。
She majors in French literature.
Literal
She [topic-は] French-literature [object-を] is-specializing-in.
専攻する ('to major in, specialize in') is the standard academic Sino-Japanese compound for declaring a field of study at university — 専 ('exclusively') + 攻 ('attack, devote oneself to'). It takes its target with を, framing the field as a direct object of focused study. The plain non-past with ~ている marks an ongoing state — 'is currently majoring' — rather than a completed event.