Collies make connections very quickly. It's best not to try to teach a collie what you mean, rather to tell it what it is doing right now and then use that word as a command for that behaviour.
If hearing you call 'Come' (or whatever your recall command is) makes her look for sheep, then you have used that command when she was looking at sheep, and she has associated the command with looking at sheep.
So what you need to practise is a word/sound that you use as she comes back to your hand. Then, after a few repetitions of this over a few days, you should start to be able to use it to get her to come to your hand.
But build it up over small distances without distractions for a while, gradually increasing the distance, or adding distractions, then both, and so on, so that by the time you use it with sheep in the picture, she's already conditioned to run to your hand.
The other thing I would also do in this situation, where I am assuming you do not want her to work sheep, is to make sure she turns to look at you when you call her name. Then, when she sees sheep, get her attention on you, not the sheep, and only then use the come-to-my-hand sound.
If you do want her to work sheep then you do not want her to look away from the sheep unless you have given her a stop working command, so the advice would be slightly different.