When Kanade goes missing Nia reminds Sei Amamiya of Hido Takafumi. Though no one suspected Hido and really seemed forgetful about him Nia is the only one who remembers how Leiji insulted him and cut him out. She challenges Sei directly that if it could be Hido that kidnapped Kanade indicating that she does see that possibility due to Amane High School's pretty narrow minded and ignorant nature at handling people as instruments rather than people. This clue allows Sei to track Hido down and find information about Kanade.
In the end she smirks at her uncle in complete satisfaction that Kanade rejected him. This could be her own personal victory over him in making him feel what she and others felt by his cold, calculative and twisted rejections and withdrawals when things didn't go his way.