Warning: spoilers. Also, slightly simplified for ease and communication.
When we first see her, Marius asks Eponine to find his new love, Cosette. Having never known love before, he challenges Love Is For Other Men d6, rolling 3d6 and adds his Relationship, Eponine Is My Greatest Friend in the Whole World d10. Eponine resists with Justice (Thems That Are Rich Deserve Nothing) d8 and her relationship with Marius which is Marius Will Be Mine d12. Eponine has dice on her side but Marius is dead keen and spends a Plot Point to also roll his new relationship Cosette Is The Most Beauteous Creature on Earth d6 and it gets him over the line. Eponine, not wanting stress, runs off to find the girl.
Later, Eponine sees her father trying to steal from Jean Valjean, having realised he can’t go to the police. Threnadier tells her to shut her mouth, she resists. Thernadier rolls Power (Master of My House) d10 and Eponine Will Do As She’s Told d6. Eponine challenges her Duty (Family Is All I Got) so she can roll 3d6 AND challenges her relationship Marius Will Be Mine so she rolls 3d12. Not surprisingly, she gets a titanic success and drives her father away. She drops both her Duty and her Marius stat down by one for the rest of the episode. At the end of the session, she rewrites that to Marius Deserves Happiness Even If That Is Without Me so she can keep it at d12.
Next Act, she finds the letter from Cosette. Even though the two never interact, the GM makes it a contest. Cosette rolls her Love d12 and her budding Marius Is My True Love stat (d8 they only just met), but Eponine rolls Truth (Everyone Lies) d12 and challenges Marius Deserves Some Happiness, rolling 3d12. She wins again and hides the letter. Because she challenged it, it drops, but at session end she changes it back to Marius Will Be Mine, so she can STILL keep it at d12.
Next session, on the barricades, seeing Marius about the be shot. Marius and Eponine challenge each other. Marius rolls Duty (I Must Suffer To Balance Out My Noble Birth) d10 and Eponine is My Best Friend In the World d10 to take the bullet. Eponine rolls Love (Is All That Matters In the End) d10 and challenges Marius Will Be Mine once more, rolling 3d12. She wins once more, and totally totally dies. Marius gives in and hands her the plot point, but she hands it back and deals him stress instead (d12 Anguish).
But she is clever. As she dies, she sings A Little Fall of Rain, relieving Marius’ stress, so he has in fact lost nothing. Eponine is a motherfucking powergamer. But nobody gives a damn because in Smallville, powergaming = drama.