Her mistake was blindingly obvious and embarrassing.

blindingly 是由动词 blind（使失明、使眼花）加上副词后缀 -ingly 构成的副词。blind 本义是"使看不见"，引申为"耀眼、刺眼"的意思。 blindingly 作为副词修饰形容词 obvious，表示程度极高，相当于"极其、非常"，带有"明显到刺眼"的夸张意味。