。
She remained silent on that issue.
Literal
She [topic-は] that issue [about-について] was-silent.
黙る ('to be silent, fall silent') in the ~ていた form describes ongoing silence — not the moment of going quiet, but the state of staying quiet over time. ~について ('about, concerning') marks the topic of the silence. In Japanese conversation, silence is itself a meaningful response — it can signal disagreement, reluctance to commit, or strategic withholding. The literal 'was silent' here often translates better as 'kept quiet' or 'said nothing' to capture this active-omission flavor.