Julia Hurstwood is George Hurstwood's wife. Like Drouet, she's basically a wannabe, longing to be part of the upper echelons of society:
Mrs. Hurstwood was the type of the woman who has ever endeavoured to shine and has been more or less chagrined at the evidences of superior capability in this direction elsewhere. Her knowledge of life extended to that little conventional round of society of which she was not—but longed to be—a member. She was not without realization already that this thing was impossible, so far as she was concerned. (9.10)
Although she may have given up these hopes for herself, she's hell-bent on making sure her kids have the chance to enter the elite social circles (partly so she can reap the benefits). "For her daughter, she hoped better things. Through Jessica she might rise a little. Through George Jrs.'s possible success she might draw to herself the privilege of pointing proudly" (9.10). To that end, Mrs. H spends much of her time trying to help daughter Jessica land a rich husband.
Hurstwood picked a real charmer in Mrs. H. She is one spiteful, calculating, and conniving lady, always thinking about what she stands to gain from any given situation:
[...] she was not a woman who would fly into a passion. She had too little faith in mankind not to know that they were erring. She was too calculating to jeopardise any advantage she might gain in the way of information by fruitless clamour. Her wrath would never wreak itself in one fell blow. She would wait and brood, studying the details and adding to them until her power might be commensurate with her desire for revenge. (12.1)
Talk about passive-aggressive, right?
Mrs. Hurstwood's tendency to turn every situation to her advantage reaches its pinnacle when she learns of Hurstwood's affair with Carrie. Her response is far from the emotional sad or angry reaction we might expect: "'I'm not dictating to you,' she returned; 'I'm telling you what I want.' The answer was so cool, so rich in bravado, that somehow it took the wind out of his sails" (22.96-97).
Her chief concern is getting as much money out of Hurstwood as she possibly can, so she blackmails him by threatening to tell his employers about the affair if he doesn't give her the money she demands. Through Mrs. Hurstwood's character, the novel explores some of the most poisonous effects of money on human relationships.