Who is Catherine from Catherine, Called Birdy and what is their importance?

The title character of the book, Catherine is a fourteen-year-old girl living in England in 1290 and 1291. She begins her journal - the book we are reading - because her brother, Edward, encourages it. Unlike most girls of her time, Catherine is extremely strong-willed and hates girlish things and especially the tasks that normally fall to women. For example, she detests spinning and weaving (and is, in fact, allowed not to do these things as long as she keeps writing in her book). She is short-tempered and often argues with her father, doing things like pushing girls she doesn't like into eel pies, or pushing her father's foster child into the river.