When presented with the lucrative investment opportunity, she didn't think twice.

didn't 是 do not 的缩写形式，表示否定。 think 的意思是"思考、考虑"。 twice 的意思是"两次"，这里 think twice 字面意思是"思考两次"。 didn't think twice 是一个固定短语，意思是"毫不犹豫"，表示做决定时非常快速果断。