How does Eliot portray the different states of mind between Godfrey and Nancy Lammeter in Silas Marner?

Godfrey's state of mind is openly described by showing all of Godfrey's fears, tribulations, and past history. Nancy, on the other hand, has a frigid personality that makes her almost impossible to read. Therefore, Eliot uses those personality traits to indirectly and directly describe the mindsets of both characters.
Godfrey is always in fear. He has followed the ways of his wayward brother, Dunstan, who fathered a child with an opium fiend and is consistently out of money. His state of mind is easy to describe because Eliot fully explains what makes Godfrey such a weakling.

Godfrey Cass was looking forward to this New Year's Eve with a foolish reckless longing, that made him half deaf to his importunate companion, Anxiety.
"Dunsey will be coming home soon: there will be a great blow-up, and how will you bribe his spite to silence?" said Anxiety.
"Oh, he won't come home before New Year's Eve, perhaps," said Godfrey; "and I shall sit by Nancy then, and dance with her, and get a kind look from her in spite of herself."

This excerpt is very telling. Anxiety rules Godfrey's days. His brother dominates him. He knows he is not worthy of Nancy. He also knows he has disappointed his father (if he ever finds out about his actions), and thinks he has basically ruined his life to a point. His brother consistently follows and preys upon Godfrey's vulnerabilities. For this reason, Godfrey manages to survive mentally from all the pressures he is under.
Nancy, on the other hand, has a cold personality that combines coquettish, prudish and sanctimonious natures together. It is hard to read Nancy, perhaps because she is definitely not the sophisticated creature that she attempts to be. Nonetheless, Nancy's mindset is the exact opposite of Godfrey's. She is not reactive or emotionally hungry. She is calm, appears way more collected than everyone else, and her icy temperament is a huge contrast to Godfrey's nature

The modest calm of Nancy's speech and manners told clearly of a mind free from all disavowed devices.

In all, Eliot demonstrates the clear differences in the states of mind of Nancy and Godfrey. Eliot is also able to identify the causes behind such mindsets. Godfrey's vulnerable personality tends to take on the wild nature of his brother, making him fail at any of his original good intentions of doing well.
Nancy, calm, proud, and much more sure of having everyone's approval, is used to being always accepted and admired; as a result, she really does not have to do much to impress herself or others. This is why her mind is "free from all disavowed devices," while Godfrey is in a consistent state of fear.