She appeared completely unembarrassed even though she was wearing pajamas at the party.

unembarrassed 是由前缀 un-（表示否定）和形容词 embarrassed（尴尬的）组成的复合形容词。embarrassed 来自动词 embarrass（使尴尬），加上 -ed 变成形容词。unembarrassed 字面意思是"不尴尬的"，引申为"自在的、不拘束的"。