。
She let out a scream of terror.
Literal
She [topic-は] fear [from-で] scream [object-を] raised.
悲鳴 ('scream') is a more clinical/dramatic word than 叫び声 — it specifically denotes a high-pitched scream of terror, pain, or anguish, while 叫び声 covers a broader range of vocal outbursts. The で here marks the cause of the scream — a use of the cause-marking で also seen in 雨で休んだ ('took the day off due to rain'). The scream comes out FROM the fear, almost as a release valve.