Let's surprise her! I think she'll really like it.
Let's shock her a little! I think she'll be really happy to hear you play.
この場合、次のような言い方ができますよ。
ーLet's surprise her! I think she'll really like it.
「娘さんをサプライズしましょう！とても喜ぶと思いますよ」
ーLet's shock her a little! I think she'll be really happy to hear you play.
「娘さんをちょっと驚かせちゃいましょう！あなたが弾いているのを聴いてとても嬉しいと思いますよ」
ご参考まで！
カナダ 
