Sitting in her armchair, Ann realized that she was by herself for the first time after many difficult weeks spent with her mother in a spotless bedroom of a Swiss hospital.

spotless 是由名词 spot（斑点、污点）加上后缀 -less（表示“没有”）构成的形容词，字面意思是“没有污点的”，引申为“一尘不染的、极其干净的”。