Mademoiselle is the loyal, loving sister of Bishop Myriel. And like him, she devotes her entire life to helping others. The novel describes her early on, saying:
She had never been pretty. Her life, which had been wholly occupied with good works, had endowed her with a kind of pallor and luminosity, and as she grew older she had acquired what may be called beauty of goodness. (188.8.131.52)
That's definitely something to strive for. Who needs Botox when you can have the beauty of goodness? Even when money becomes tight in the household because of her brother's generosity, she writes to a friend: "I am as happy as ever. My brother is so good. He gives everything he has to the sick and needy. We never have enough" (184.108.40.206).
Like her brother, Mademoiselle is practically a saint, and whenever her brother's faith wanes, she's always there to support him and help him push onward. Interesting character? Not really. Good person? You bet.