i have complained countless times to my manager about being bullied by a co worker. My manager has made this coworker second in charge now after i stepped down from the position due to my manager not training me. (my manager is terrible at her job but that's a different story). the coworker is even worse now! the power has gone to this person head, she loves confrontation and now that she is second in charge she literately tries to have full blown arguments with me for no reason because she thinks she can. although the way she approaches this makes me feel like I am being attacked and i feel overwhelmed and red faced. and feels like she puts me in the position where i need to think of comebacks to her words because thats how she speaks me. - i dont use come backs by the way as i am very aware she is trying to get arise out me and im unsure with the whole situation during because there is no topic (just nonsense).

anyways my last complaint to my manager i added that i will not work with her anymore (ile be doing 12hrs per week due to uni so it shouldnt be that hard) or she can move me to a different department. and if these arent possible after exploring these options then i will put in my 2 weeks notice. she got back to me 5 days later after i asked her half way through my shift... she said she cant move me so i will have to put up with her. i said that i will try to speak to other managers about it. i then asked my manager if she will be doing anything about the coworker and she said no.

i expressed my concerns saying that 2 people have quit because of her and one person 1 day prior to my requests threaten to quit. also others feeling comfortable with her to say that this coworker is hard to work with. and that she should at least make a team meeting so we can all express our feelings and problems regarding the department because it has been falling apart for a long time. ... my manager went all red faced and dribbled words i couldn't even explain but she did not agree.

what is my manager obligated to do when the problem is clear as day and there has been complaints said directly to her?