Flora is two years younger than her brother (she's eight), and is just as adorable; the two of them are often compared to angels, and their beauty is their most prominent quality. Both of them seemingly cast a spell on the Governess just by merit of looking the way they do. Flora meets the Governess first, and though we don't see as much conversation between the two of them, we know that the little girl instantly wins the affection and adoration of her teacher. However, once Miles enters the scene, Flora kind of falls by the wayside.
If we know little about Miles, we know even less about Flora. Basically, all we get is that she's only slightly less compelling than her fabulous brother – and that, we might guess, is simply because she's a girl. Miles's male-ness is what allows him to be forgiven time and time again by Mrs. Grose and the Governess, whereas Flora is the first to fall under suspicion. Notably, she's also dismissed by the Governess after the second lake incident, while the older woman stays with Miles to try and salvage him.