Earthlock: Festival of Magic

Story related, cannot be missed.

Olia is the red-haired girl that had joined your party during Ramoo but had left your party when you made it to the Burning Desert. When you arrive at the majestic City On The Ocean, Suvia, a cutscene will trigger. After this scene, head to the right to trigger another cutscene near the fountain. Here, Gnart will suggest that you should head to the Owl Tide and Lady Lumia. She might know some information about the artifact and Benjo's whereabouts. The House of the Owl Tide is north of the fountain, head straight up ahead and enter the building that you see.

When you enter, you'll be inside the Owl Tide Library, the House of Wisdom. The High Owl is in her garden which is found in the top left corner door. Enter through this door and a cutscene will trigger where you'll see Olia and Lady Lumia having a conversation. Gnart will introduce your party to her and as the conversation goes on about the cult and the Aderyn woman. Olia will rejoin your party (this time permanently) after the cutscene comes to an end, unlocking the trophy.