。
She still doesn't know the truth.
Literal
[topic-は] still truth [object-を] does-not-know.
真実 ('truth, reality') is the formal/literary noun for 'the truth' — heavier than 本当のこと ('the truth' colloquially), more abstract than 事実 ('the facts, factual reality'). The verb 知る ('come to know') in its plain negative 知らない gives 'does not know,' which matches the まだ ('not yet') frame naturally — まだ知らない = 'does not yet know.' Note that for affirmatives Japanese requires 知っている ('be in a state of knowing') — but for negatives, plain 知らない works (since 'not yet having entered the state of knowing' is just 'not knowing'). Common dramatic line — implying that she's about to find out, or that someone has been protecting her from the truth.