Does your yearling know how to "send"? I'm prepping my yearling for trailer loading, so it's imperative that she gets used to stepping up or onto scary objects. Take her out and learn how to send her down a fence line, kind of like ground-driving, but standing still. You should point in a direction, and she should go in that direction. If she doesn't, reinforce with the end of your leadrope, carrot-stick, or whatever you have. You can probably look up sending exercises in the NH pages.
Then take her out and send her over poles. Send her over a piece of wood. Send her over a tarp. She has to go where you send her with confidence. Moving backwards or stalling out is not an option, she must move forward and come off the pressure, even in a scary situation.
You can even ask her to come into pressure. I will stand in front of my yearling, pull forward. If she does not move forward, I will add pressure by spinning my rope rhythmically next to her. If she steps forward, I stop spinning and release pressure. When I'm in a tight spot, like a trailer or barn aisle, I can ask her to come forward with emphasis by spinning my rope and encouraging her to come through pressure.