In 2021, she edited an anthology called Horse Girls: Recovering, Aspiring, and Devoted Riders Redefine the Iconic Bond, with Harper Perennial.

Marcus rode horses in high school but stopped in college and adulthood; she felt at a crossroads with the discipline and also found it difficult to maintain due to financial, educational, and time constraints.

The section's premise was to publish a fiction piece for free once a week on Tumblr, a model that sought to combine a sense of editorial curation with more modern trends in media distribution on the internet.

[3] In 2021, Marcus released an anthology she edited, called Horse Girls: Recovering, Aspiring, and Devoted Riders Redefine the Iconic Bond, published by Harper Perennial.

Publishers Weekly gave the book a starred review and included it in their top picks, stating: "The essays are tender, critical, and deeply personal, and the universal themes of growth and belonging come through consistently but, refreshingly, never feel repetitive.