。
She doesn't know much about the world.
Literal
[topic-は] things [object-を] doesn't-know.
ものを知らない is an idiomatic phrase — literally 'doesn't know things,' but functionally meaning 'is naive, unworldly, ignorant of how things work.' This isn't about specific factual gaps but about a general lack of life experience or worldly wisdom. Compare 何も知らない ('doesn't know anything') which is more concrete. The phrase often carries a lightly disapproving or pitying tone.