I stand outside the trailer and have the horse walk on. I’m not a fan of leading horses on unless it is an unfamiliar horse and there are two people. I don’t know how well this works for a slant load.
I stand on the ground beside the ramp and have a long enough whip to touch above the tail, the hock, the fetlock, or whatever works best for a particular horse. In a step up, I’d stand on the side closest to the edge of the trailer so the horse can’t swing his hindquarters all the way around until he’s facing backwards. I throw the end of the shank over the back of the horse, and I can always grab it if the horse moves backwards. It’s important to stay out of kicking/striking range.
A relaxed, confident attitude is key. You already realize that your sense of limited time wasn’t helpful. When you take her out next time, allow yourself more time for loading up before coming home.
If I know the horse isn’t scared and he/she just balks, I’ll first signal with the whip, make noise, etc. If they stay stubborn, I’ll smart them above the tail, on the rump, on the hock, or on the fetlock depending on what works for a particular horse. Standing still is not an option, and I’ll work until I figure out what motivates that horse.
Reward any sign of “forward” by stopping the cue and relaxing your body posture. So if the horse stretches her neck forward looking into the trailer, she immediately gets a reward. They catch on to this quickly. If she stands like that without appearing to be thinking about moving forward, resume the cue. Leaning forward also counts, unless the horse stands that way for a long time. Wait a reasonable time and ask for “forward” again. Do not cue at all while the horse is actively moving forward.
Some people circle the horse to point them straight forward. I figure that any time we allow them to turn their front end away from the trailer, they have a sense of winning a battle. It’s counter productive. If a horse isn’t pointed straight in, I ask them to swing the hindquarters around rather than leading them in a circle. Also, if you’ve got a helper on the trailer, it really helps to not allow them to turn their head away–I like to have their heads toward/in the trailer no matter what the feet are doing.
Hopefully, she’ll be absolutely fine after this one episode. However, if she decides she won some kind of battle, it could escalate. Then you need to plan out your tactics, how YOU like to load, and work from there. Horses can learn the same thing in a variety of ways, so the trick is to figure out what works consistently for both of you.