Millie grows

Our young sheep dog is growing well, now at 5 months she is just starting to take commands and shows interest in sheep.I'm thinking of introducing her to sheep over the next four weeks or so, I just need to make sure that the sheep I use are used to dogs to avoid any chance of putting Millie off sheep for good by getting butted.
Not sure what's going on with those ears, one day they both looked pricked the next both down then one up one down.