。
She's going to be surprised.
Literal
She [topic-は] surely will-be-surprised.
驚く ('be surprised, be startled') is intransitive in Japanese — the experiencer is the subject. Compare to the transitive partner 驚かす ('surprise, startle [someone]'), where the agent is doing the surprising. This intransitive/transitive split is one of the most pervasive features of Japanese verb morphology, with paired verbs covering most action-state distinctions: 開く/開ける, 落ちる/落とす, 始まる/始める, 驚く/驚かす. The bare future form 驚く paired with きっと is a confident projection.