What are some characteristics of Miranda?

When Katherine Anne Porter's short story "Old Mortality" opens, one of the characters, Miranda, is just eight years old. But she feels much older:

 Maria and Miranda, aged twelve and eight years, knew they were young, though they felt they had lived a long time. They had lived not only their own years; but their memories, it seemed to them, began years before they were born, in the lives of the grown-ups around them, old people above forty, most of them, who had a way of insisting that they too had been young once. It was hard to believe.

Right off the bat, we can see that Miranda is mature  beyond her years, that she is highly observant, and that she knows how to behave around adults. 

We see these characteristics quite clearly in another scene, in which the two sisters watch their grandmother crying over old keepsakes during one of her periodic spells of sentimentality:

If Maria and Miranda were very quiet, and touched nothing until it was offered, they might sit by her at these times, or come and go. There was a tacit understanding that her grief was strictly her own, and must not be noticed or mentioned.

We also see that Miranda aspires to great beauty, and that she is concerned with outward image:

Miranda persisted through her childhood in believing, in spite of her smallness, thinness, her little snubby nose saddled with freckles, her speckled gray eyes and habitual tantrums, that by some miracle she would grow into a tall, cream-colored brunette, like Cousin Isabel; she decided always to wear a trailing white satin gown.

Later, when she's a bit older, Miranda is an avid reader:

During vacation on their grandmother’s farm, Maria and Miranda, who read as naturally and constantly as ponies crop grass...

And we learn that she's ambitious:

Her hope of being a beauty died hard, until the notion of being a jockey came suddenly and filled all her thoughts. Quietly, blissfully, at night before she slept, and too often in the daytime when she should have been studying, she planned her career as a jockey. It was dim in detail, but brilliant at the right distance. 

Again and again, we'll see examples of how detail-oriented Miranda is, and how much she pays attention to things that might escape others' notice:

The jockeys sat bowed and relaxed, their faces calm, moving a little at the waist with the movement of their horses. Miranda noted this for future use; that was the way you came in from a race, easy and quiet, whether you had won or lost.