Thread: Working dog

Sounds a bit like she is changing her habits to suit herself a bit now
Either she is misinterpreting her "push" command or is just deciding to give them a good old chase around. Do you ever get her to bring the cows toward you while you are reeling the reel in to give them a new break ? could be she forgets if she is supposed to be bringing them to you, or push them away.
It can be an age where they think they should be making the decisions Try a bit of obedience work just before you get the cows. Sit, come etc... and see if that helps.
Otherwise maybe a bit of reinforcement with the commands, to remind her what you want and re-establish her need to listen.