She is a meek and mild mannered member of the academy Lelouch, the main character, attends.
During a day off, she and some others go on a trip or something. They end up being taken hostage by the Japanese Liberation front and are threated to be killed. The bitch (Nina) doesn't take this well and further develops her fear of the Japanese, which was already present.
One of the other hostages is the disguised princess Euphemia. She voluntarily reveals her identiy so that the JLF focuses on her rather than the hostages. Nina, who was already having a nervous breakdown looks at Euphie as some kind of savior and is unrealisticly attached to her from then onward, going to far as to masturbate using a table corner and a picture of Euphie in a news magazine.
Lelouch is eventually forced to kill Euhphie, and this sends Nina off the deep end as she no longer has her idol. She goes crazy and has remained crazy since this season began.