Julia is plump and ordinary-looking, but is expected to be looker like her father when she grows up. For now, probably as a side-effect of her plumpness, she is pale, and has a tendency to breathe heavily. She is not allowed marmalade, which is not surprising considering how much she piles on when she gets the chance.
She is learning witchcraft from Michael Saunders. When she casts a spell, she ties a knot in her handkerchief, and the spell lasts until she unties the knot.
Despite being under orders not to use magic without adult supervision, she and Roger often animate their toy soldiers when they play with them. The battles invariably end with Julia's soldiers running away; she says this is because that's what she'd do in their place.
She reads thrilling adventures stories with titles like In the Hands of the Lamas.