She was decked out in her nicest outfit for the party.

她穿着她最漂亮的衣服去参加这派对。

deck out这个词组表示装饰，打扮。用...装饰后要接介词with或用...打扮后面要接介词in。

The room is decked out with a lot of small lights.
这房间装饰着许多的小灯。