Problems at work

I have been having issues at work with one individual. I only work with her one day a week but when I do she's extremely rude and bitchy. She is a supervisor when there's not s designated supervisor around. Usually there is thankfully but sometimes there's not. 
When there isn't she gets super over bearing and 'power crazy' and for awhile I thought it was just me she was going after...another supervisor on the same level as her noticed something but can't do anything about it. Well yesterday there wasn't another supervisor above her for a couple hours and she wouldn't get off my back, another co worker of mine walked up and said  she's really frustrated with the 'supervisor' and says she feels picked on by her and it makes her not want to be there or come to work on this specific day that she's I finally emailed my manager saying myself and another coworker have had issues with this person.....that was last night and my manager emailed back and said she wants to sit down with myself, coworker, supervisor and the supervisor who comes in later and works with all us. And for some reason I'm nervous!?