Despite his explanations, she remained unconvinced by his excuses.

unconvinced 是由前缀 un-（表示"不"）和动词 convince（使信服）的过去分词 convinced 组合而成。convinced 表示"被说服的"，加上否定前缀 un- 后表示"未被说服的、仍然怀疑的"。