I'm confused

It’s in the novel. She always carried a bouquet of camellias, either red or white. The five days a month she carried red ones most likely refers to menstruation, indicating that she was not available for sex.

From the original french:

Marguerite assistait à toutes les premières représentations et passait toutes ses soirées au spectacle ou au bal. Chaque fois que l'on jouait une pièce nouvelle, on était sûr de l'y voir, avec trois choses qui ne la quittaient jamais, et qui occupaient toujours le devant de sa loge de rez-de-chaussée: sa lorgnette, un sac de bonbons et un bouquet de camélias.

Pendant vingt-cinq jours du mois, les camélias étaient blancs, et pendant cinq ils étaient rouges; on n'a jamais su la raison de cette variété de couleurs, que je signale sans pouvoir l'expliquer, et que les habitués des théâtres où elle allait le plus fréquemment et ses amis avaient remarquée comme moi (2e ch., La dame aux camélias par Alexandre Dumas, fils).

Marguerite was always present at every first night, and passed every evening either at the theatre or the ball. Whenever there was a new piece she was certain to be seen, and she invariably had three things with her on the ledge of her ground-floor box: her opera-glass, a bag of sweets, and a bouquet of camellias.

For twenty-five days of the month the camellias were white, and for five they were red; no one ever knew the reason of this change of colour, which I mention though I can not explain it; it was noticed both by her friends and by the habitués of the theatres to which she most often went. She was never seen with any flowers but camellias. At the florist’s, Madame Barjon’s, she had come to be called “the Lady of the Camellias,” and the name stuck to her (ch.2, Camille by Alexandre Dumas, fils, translated by Sir Edmond Gosse).