DonnEll
Why did souta even brought her if they separate and what if heili use the escape talisman she just will be outside alone and there is no point in taking her. What's the difference of leave her in the inn? Oh I know because there's magical situation that make her power up just in instant
The point is to show that souta didn't know everything. Alexander didn't tell him everything about this place, only the basic. Not every character that souta met will become major one. Some will just pass by even with his help. Even if she advance to a rank, it was still nothing to souta. He just helped her because he could there's no other meaning. Also this realm is alexander the one who will receive greatest benefit in this place is him.