I understand the idea of the long line. Let's see if I can make sense about what I think may be going on here
I want a horse to want to find safety with me. I want a horse to know being away from me is not a safe place to be. I want a horse to worry more about what I will do, more than they worry what anything else can do to them. Make any sense to you?
A Leadmare with a naughty herd member will put that member out on the far reaches away from the herd and safety. (Like the rail of the round pen to you.) Leadmare doesn't touch that member unless it challenges her up close and in her personal space and then she means what she says

. She controls from long distance with body language that is very clear to the offender. She will walk, maybe trot in small circles, while the offender is running stupid on the out skirts. She will not let it stop until she knows she has the offenders wind. She may not even let the offender back in the herd for days. She demands the respect she is due and makes it very unpleasant to be out of her protection.
So far make sense?
Now, in your herd, Pris is the leadmare and your trying to take over this position. Is she going to fight back? Oh yeah, and she will be a tough nut to crack. And being a pony, it's a little tougher as they are always more determined to be the boss.

I find that when the bad behavior shows up, it's because we are making their place in the herd not so clear to them. Kinda like smacking the queens crown off her head

She's going to try to keep it. Before this she was going along with you, because she was enjoying it. Now it's becoming work and involves someone else being in charge and it's not so fun anymore
Now by putting her on the rail and making her move her feet, you are asserting your leadership and she's thinking "Hey, wait a minute!"

and then acting out the "NO!" she's saying with the charging, kicking and biting crap.
Sometimes it's safer to take them and turn them loose in a larger arena and do the driving there. Not quite as confining for the person. You don't have to run, but she has to shuffle her feet fast enough to make an impact on her wind.
I just tend to approach it a little different. While free lunging she can keep her nose out there and as long as she is moving faster than a walk, I'll just sip my coffee. When a horse or pony "loses their mind" as I call it, I go back to the very beginning and act like it's a colt that has no sense or idea of what it's supposed to do.
I don't care if she's changing gaits, looking at the moon, sucking her thumb. As long as she keeps moving. If she slows to a walk, make her trot at min. It may take five minutes it may take an hour, five hours, but at some point she's gonna look at you. This is where you need to read whether she needs more pressure to keep her moving, or is she wanting relief. If you offer relief, and she gives the slightest bit of hesitancy, move her feet again.
I call this "taking her wind." You can take a horses food, water, companionship, or freedom and you may never get their mind. But take their wind, control when they can rest to get their breath and they start to think of easier ways.
By not using the line the horse is making his own "Choice" of your worthiness to be his/her leader. Of course, your ability to out think them helps them make the right decision
