。
She was startled to see a black cat.
Literal
She [topic-は] black-cat [object-を] saw-and was-surprised.
見て驚く is a stock pattern — perception verb in te-form chained to a reaction verb. The te-form here marks cause or trigger: 'seeing X, was surprised by it.' Black cats hold a complicated symbolic place: in much of the Western tradition they're omens of bad luck, while in Edo-period Japan a black cat (黒猫) was sometimes considered auspicious, especially for women's prosperity and protection from illness. Modern Japan has absorbed both readings, so reactions vary by context. The verb 驚く itself is intransitive and takes the surprise trigger with に or via te-form chaining, never with を.