Cow Dog Question

I am having an issue with a dog I recently started on cattle, and figured I would ask here too.

She bays loose, doesn't mess with settled cattle anymore (after a couple verbal corrections early on), however yesterday she was in the pasture on two different heifers that I had to rope. Once they were roped, she was catching them. This same dog when baying hogs is a loose dog, but will help once the catch dog catches. I just told her to get out in a firm voice, it took getting onto her several times to get her to back off of them. She then did it on the second heifer I roped... You think a trashbreaker is the answer here?

Second question:

What is a common command used for the dogs to back up, so that I can push through a gate, or just to let up some pressure? I have a tendency to tell her to "get out" When I tell her that, she quits the cattle and walks away, then I have to put her back on them. It's almost like an on/off switch, when what I really need is a dimmer.