@Madyona She is a person that is high in agreeableness. That makes her pleasant to be around since she will go along with things, but it also makes her quite unable to hold her own in arguments. Someone that is more disagreeable would be overpowering in arguments by the sheer amount of stuff they can say.
So even if she knows she has to speak up, she is unable to since she lived being too agreeable all her life. That is also why the ML was able to rope her in so easily just by being a little pushy.
There is a lesson to be learned here, don't go along with everything others do or say in order to avoid conflict, or you will be giving yourself up.