。
She knows Japanese history well.
Literal
She [topic-は] Japan's history [object-を] well is-knowing.
知っている describes a knowing-state, not the action of learning. The plain 知る ('come to know') is the inceptive 'find out'; ~ている expresses the resulting state of having that knowledge. Without ~ている, 知る in the present would be unnatural for ongoing knowledge.