Despite doctors' explanations, she still held the delusion that she was being followed.

delusion 是名词，来自动词 delude（欺骗、迷惑），指"错误的信念或想法"，特别是那种即使面对明显相反的证据也坚持的错误想法。在心理学上特指"妄想"，是一种病态的心理状态。