She would be experienced in household matters, and would understand the bringing up of children.
"Julia's father, on the other hand, was a retired sea-captain.

Seafaring folk are generally loose sort of fish.

He had probably been in the habit of going about the house, using language and expressing views, the hearing of which could not but have exercised an injurious effect upon the formation of a growing girl's character.

Juliana was his only child.
Only children generally make bad men and women.

They are allowed to have their own way too much.