This achievement is story-related and can't be missed.
At some point halfway of the story you'll need to go to Suvia, the main city of Umbra, where you'll meet Olia again. She'll be automatically added to the party and the achievement should unlock right away.
If you are struggling to get to Suvia you can either take your time to better develop you characters so they can face enemies on your way to Suvia or you can simply rush and play dead, flee from the fights. I'd prefer the first approach, since you'll need strong character late in the game anyways.