Marks was a therapist, hypnotizing patients and turning them into the Spirit of the Goat.
Dr. Marks was a therapist to both Randall Milkie and Raymond Earl hypnotizing both into becoming the Spirit of the Goat. She believed that the rich and powerful had gunned down all hope in the city, and hypnotized the custodians into becoming the Spirit of the Goat to murder the first born children of Gotham's wealthiest citizens. Detective Bullock later discovered this after seeing Raymond Earl display the same hand clenching movement as Robert Hastings. After being discovered, she attempted to have Hastings kill Bullock. After a brainwashed Hastings was beaten, she tried to escape only to be shot in the leg by Bullock in the process which led to her arrest.
Both of Dr. Marks proxies, i.e. Randall Milkie and Raymond Earl, worked at maintenance companies that served the wealthiest of Gotham's families, literally giving them keys to the door and allowing them to enter without breaking in. They would dress up in a black leather outfit with horns on top, abduct the first-born child of the family, and take them to a local historical landmark. There, they dressed them in white, hung them up by their arms, killed them by asphyxiation, and lit several candles at their feet as a shrine. Finally, he would sew an 1830 Liberty penny into their heads.