Leni is not selfless. But she has, in order to accept her imminent death stopped wanting things for herself. Arguing that if she wants things, it will be too painful to admit she’ll never have them. So she suppresses any want or desire she has into things for other people.
Here is an excerpt I wrote about her...although I haven't figured out what to do with it. It takes place about a year prior to anything in the actual novel:
Leni sighed, this was the worst part. Watching all of the other sacrifices enter the field. Most of them dressed in the best clothes they could afford, thinking a show of wealth would help them. Ages ranged from six to sixteen, although younger children could enter, could be forced to enter, as Leni knew all too well. Leni could see the tear streaked faces, she could smell the fear radiating off those around her.
She closed her eyes. She didn't need to watch to know the elderly priest took the stage. To know the motions of the blessing, to hear the familiar chant. She had done this before. It was to be her twelfth time to go through the trial, one year more than anyone thought she would have to endure, but they had changed the law, and now you aged out at 17.
The chant ended, and she heard the priest say "Now we pray". Leni smiled, slightly, she knew the prayer, but said her own, in her head.
"Oh Goddess of Death and Judgment, I am already dead" I'sald, I have forsaken you.
"The crimes I have committed against you have stripped my soul" I will not ask you for mercy, or apologize. I do not deserve mercy.
"My flesh remains. Reclaim what is yours. I await your judgment of my guilt" I am guilty of the crimes against me. I have killed, I will kill again.
"Oh Goddess of Souls, rejoin my body, rejoin my flesh and soul, decide my fate" All I ask of you, is to spare the others, they have not lived. They are children.
"Let me take another turn on the wheel" Give me another turn on the wheel and give them back their lives.
"Bring me home, to honor you" If you have honor you will do as I ask, and give Ame the strength to understand.