In 2012, Hartema took part in the seventh season of ProSieben's Germany's Next Topmodel, presented by Heidi Klum, which 15,700 candidates applied for.

She quickly became a stand-out candidate for her modeling potential, which was praised by the judges as well as by all the clients that appeared in the show, but her lack of self-confidence was criticized by the judges at the same time.

She won the competition in the live finale on 7 June 2012 at the Lanxess Arena in Cologne, beating Sarah-Anessa Hitzschke, Dominique Miller and Kasia Lenhardt.

As her prizes for winning, she received a cover of German Cosmopolitan, a temporary apartment stay in a fashion metropolis of her choice, campaigns with Emmi Caffè Latte, Maybelline Jade and Zalando, and a contract with OneEins Management.

In 2012, she appeared in the music video for Hurricane Dean's "Appeal".