Just an update.   Taking on board what you said. We had boarder collie come visit us. “sneak”  our bitch changed to some degree. Even though the visiting dog had no stock skills. Sneak was very keen to get to the sheep.
She did not really push them but showed some push and bite on a few occasions. She did a good run with a nice outrun and cast to block them when the took off from one paddock to the next. Then pushed them trough a gate when we returned them. All with out a word except Go!
Thanks again.

Answer:   There is nothing wrong with you being in the middle of the flock when you’re working a dog.  Bud often did this for various reasons.  It does more harm than good for you to go to the back where Sneak is and help her move the sheep, but perhaps you can set something up with you in the middle of the flock, driving most of them so she is encouraged to bring the rest along . . .?  Just keep your eyes open and think creatively.