I tried Sprite next on shedding the large group out away from a fence (ok, it's not that large, but it's the bigger than the small group). She did it just right the first time which I was not expecting. I made a hole for her, called her in, she came in and turned on to the sheep I was facing and drove them away. I thought it might be fluke so I tried it again and no, it wasn't a fluke. I guess she knows it. I could make it harder with stickier or smaller groups, or not making the hole for her, but I think I'll stick with our success for now.