Fantine is my favorite female character in Les Mis, although I liked her better in the book (not shocking, as there's more room for characterization in a novel than in a musical). Congratulations!
Anyway, Fantine is an extremely loving character. She adored Cosette's father (not present in the musical, but alluded to in "I Dreamed a Dream"), and she loves Cosette with all her heart. Every move she makes is for the benefit of her daughter, and there's a kind of desperation to give her a good life. There's also a desperation in her still-existing love for Cosette's father, even though he abandoned her. She's too naive for her own good (giving Cosette to the Thenardiers, in hoping they would provide her with a good home), and was a virgin until she met the father of Cosette (again: only alluded to in the musical, but I don't remember if that was in the book or not... it's been a while since the last time I read the entire thing)- which (to me) makes her turning to prostitution even more striking- as it shows just the lengths she will go to for Cosette.
As for her death scene, there's always that decision to fade out on the last line ("and tell Cosette I love her and I'll see her when I wake"), as Ruthie Henshall did in the Tenth Anniversary Cast, or belt it, as Randy Graff did in the OBC. Your director may point you which way to go with that; I think both ways work fine.
Congratulations again!