Mc was kinda dumb here. It was kinda obvious she was lying from that stupid grin on her face. She wanted you to die for a reason. She watched so she could make sure you died. She even opened the poisoned and forced you to inhale it so you would just take it right then and there.
Well, as all manhuas like this, she's dumb and then regains her braincells right as she is reborn so no dumb mc anymore, yay!