。
She was unable to express her opinion.
Literal
She [topic-は] own opinion [object-を] state [nominalizer-こと] [subject-が] could-not-do.
自分の意見を述べる (to state one's own opinion) uses the formal 述べる (to state/express). ことができなかった is the past potential negative — she was unable to do so. The sentence implies either a lack of opportunity, courage, or language ability. 意見 (いけん) is the standard word for an opinion or view.