。
She was paralyzed with fear.
Literal
She [topic-は] fear [from-で] was-frightened.
おびえる ('to be frightened, cower in fear') captures fear-induced paralysis — the freeze response, distinct from active panic. The verb originally meant 'to startle, be startled' but has narrowed to specifically describe the trembling, cowering kind of fear. ~ていた (resulting state in past) frames it as a held condition, not a momentary reaction. Pair the で-marked cause with the verb's particular flavor and you get a complete vignette: fear holds her in place.