Her own person and disposition at 10

We get a description of Catherine's person and character at two stages. First at age ten.

It's a familiar bit of literary real estate to us. She is an unattractive, gawky girl, a bit of a tomboy.
She has trouble learning, or does she. Here we have the Austen wit at its best.

She never could learn or understand anything before she was taught; and some times not even then, for she was often inattentive, and sometimes stupid.

This is familiar territory to anyone who has read a lot of books intended for girls and women. This is Anne Shirley. This is also more or less the description of the heroine of any Sophie Kinsella or Emily Giffin novel. We know this girl or young woman and, more than that, we can identify with her because she is like us. Most notably, I think we can see Austen exploring the territory out of which she will fashion Elizabeth Bennett here. (But very much not Elinor Dashwood or Fanny Price.)

Elizabeth Bennett is a poor musician, although we begin to suspect better than she thinks. Marianne Dashwood is a brilliant musician and Elinor Dashwood can draw. Catherine Morland can neither play music nor draw! She has some enthusiasm for drawing but never gets to be any good at it.

And then the punch line:

What a strange, unaccountable character! — for with all these symptoms of profligacy at ten years old, she had neither a bad heart nor a bad temper; was seldom stubborn, scarcely ever quarrelsome, and very kind to the little ones, with few interruptions of tyranny ...

Despite being nothing that ideal accounts would have a young woman be, Catherine Morland has a good character. In the Aristotelian tradition of ethical thinking, of which Austen is one of the greatest representatives, this is crucial. Someone who has not been raised well cannot learn anything about morality. Catherine can.