Mrs McGillicuddy saw a woman being strangled on a train and, in spite of everybody seeming not to believe her, she insisted that she was right and, with her friend's help, proved it.

insisted 是动词 insist 的过去式，insist 由前缀 in-（表示"加强"）和词根 sist（来自拉丁语 stare，意为"站立"）组成，字面意思是"坚定地站立"，引申为"坚持、坚决主张"的意思。在这里表示麦吉利卡迪夫人坚持自己的说法是正确的。