She was suffering from a complex that made her think everyone was talking about her.

complex 在这里是名词，指"情结"，心理学上指由潜意识中的情感、记忆等形成的心理状态，会影响人的行为和想法。这个词来自拉丁语，原意是"交织在一起"，引申为"复杂的心理状态"。