Seperation anxiety like this gets harder to fix the longer you let it go on. At shows she should never truly be alone, there should be other cattle in the vicinity, the only time she should be alone truly is on the trailer. Unfortunately, really the only way to fix this is to seperate her and let her get used to it. She will probably ball, go off feed a little, pace, etc. But you just have to let them work through it. I would start by getting the other calf out of the pen with her, maybe start by putting them in adjoining pens. Its ok for her to have a barn buddy, but she has to learn to not depend on them, maybe change calves that are in the pen next to her occasionally so she doesnt get attached to one calf. When you are working with her, try to find a spot like in a barn, behind a barn, somewhere where you can tie her and she cant see the other cattle. Slowly increase the time she stays seperated. Like I said its ok to have a barn buddy, most cattle actually do better and grow better if they arent the only one in the barn. And many times with cattle its not so much being alone that is the biggest issue for them, though they are herd animals and like having a buddy around wether that buddy is another calf, goat, horse, chicken, you, or whatever. But many times when we see the sever fits with seperation its not so much the seperation in general as it is them being seperated from a buddy they were very attached to.
But like I said, unfortunately the only way to fix the problem is to seperate her and let her work through her tantrum and get used to it.
New to showing need help with show stick