My sister going though the same thing and i dont know how to help her
You can't help her until her coworkers call out the abuser. Unless everyone at the work is abusing her or ignoring the abuse, in that case she should change jobs. I got lucky, my coworkers saw what was happening, said it to the abuser, the abuser left the job and now we just talk about how shitty she was once in awhile in get-togethers.
As for emotional damage, a therapist helped alot for me. She thought me that I can't be and shouldn't be liked by everyone, there will always be some who don't like me or don't agree with me. I should not go out of my way trying to please everyone and make everyone happy.
I had a senior coworker just like that, she singled me out and always criticized me, told me to do impossible tasks in impossibly short times... I was still new there and I was supposed to listen to her and learn from her, but according to her I was the worst of the newcommers. I went home feeling like a failure every day. I mean, why is she mean with me, but nice to others? Must be my fault, right? After everyone else noticed and called her out, I realized she was verbally and emotionally abusing me for no reason. I was actually the best of the newcomers. Thank god she left. But she did lots of damage to my self esteem, I still question everything I do and I self-criticize myself alot. These kinds of people are super toxic.