Omg! That's what i thought! Cos u know.. when they talked... his eyes... the shading... yea. But my thought process was. He used charming magic on her to bring her into the party because of her quality potions. But when he found out she was e-rank he wanted her out...? Maybe.. idk.
I bet that asshole "hero" used some kind of charming spell on her to make her come with them and them going up the ranks only thanks to her (╬ ̄皿 ̄)