How do Kor’s experiences at the trial relate to her ideas about justice?

I think that Kor wanted to both see and experience justice for Jews in the holocaust. She wanted to be a part of that unique experience:

Kor says the experience for her, a survivor of Auschwitz who used to be called a "dirty Jew," to sit in a German court and be treated with respect by German judges and attorneys and the German court system was a little bit surreal.

"I could at times pinch myself."

I think beyond that, Justice meant the ability to extend forgiveness to the repentant Oskar Groening so there is also healing on both sides.