Green Prison!
Lagartha cast her domain spell after getting close to Arto. A dome of green vines was created out of thin air, separating herself and Arto from the rest of the rankers. It was the same spell she had used on Eren once. Now that she was in the Awakened rank, she could truly exert her domain power.
She could strengthen all her wood-element spells inside the domain. Plus, it would allow her an enhanced recovery rate, preventing her from getting slowed down by serious injuries.
She was only at the beginning of her Awakened rank, while Arto was only a few steps away from reaching Arch rank. Arto's weapon proficiency alone was a deterrent on its own. Furthermore, he was a veteran fighter who dealt with demonic ranker subjugation raids in the past. His experiences as a veteran ranker couldn't be ignored.