Speculation: she comes from a family with expectations she could not meet, so she ran away and became the "saviour" of this village and felt like she belonged somewhere; now she is afraid of losing everything because of the new lord as people stop relying on her.
Not like there isn't plenty to choose from. We have the loli healer and kinda childhood friend. A well meaning clutz that cooks. A prim and proper warrior. Maybe the MC will end up with all four, because manga logic.
He's going for the classic manga "good-natured" people, which in reality translates to naive morons. Still, of all the people here, she's by far the most stupid. She and the village would be screwed if she actually managed to kill Oscar.