I don’t recommend dragging one, as it can set you up for a horse in your lap if the horse suddenly decides to “give” and jumps forward, as well as pop the horn off your saddle, if you’re not using a roping saddle.
The toe in the belly trick does work pretty well for sulky horses that don’t want to move forward, but you need a pony horse that’s pretty handy, and even better if they’re willing to kind of shoulder in to the horse on a small circle and move it around (think circling up in working cow horse, but much slower). Basically, you’re pushing the ponied horse around and getting them to get the idea that they are on the bottom of this pecking order of 3, and need to do what is asked. If the horse is really being sulky, you can use the toe of your boot in the side of the ponied horse, while pushing it around in the small circle. That seems to work the best for horses that are just being obnoxious, not truly ignorant horses that don’t know how to lead well.
Riding figures-- serpentines, circles, squares-- can also help the ponied horse learn to follow the pressure of the lead, stay in the proper spot, and keeps their brain engaged. It will also help you get a feel for handling the rope and reins, coordinating your cues to the horse you’re riding and the horse you’re leading and get more confident with your ability to maneuver them. Like everything with horses, ponying requires some skill and some feel, and you only get that by practicing. Also, make sure to practice “whoa” a lot from a walk and trot before ever moving up to a canter, so you don’t end up with something like a hooked marlin the first time.
I’ve ponied quite a few horses, and most horses that have good ground manners and lead well will take to being ponied pretty quick, but some have an attitude about it. It seems that horses that want to be the top of the herd order particularly get an attitude about being ponied and will need more work being pushed around and having their body parts moved before they will just go forward with good manners.
For equipment, I like a rope halter with a good yacht braid lead rope that is attached directly to the halter. I don’t like snaps to break or hit the horse in the jaw, and the yacht braid is a nice size to handle with good weight so it doesn’t fly around. I like the rope halters because the rope has a little bite on the poll or over the nose if the horse is being naughty, but won’t bind up like a chain that is threaded though a regular halter can. Always, always use gloves. I’ve had 2d degree burns on my hands from rope burns from a naughty horse (not ponying, but handwalking a stall bound rehab), and it’s no fun.
Just take it one step at a time. I’m sure when she started being line driven, she didn’t just get the reins clipped on and then went forward in a straight line down the wooded path in a lovely frame. You probably started with lunging, then put lines on and went in a circle, and gradually worked up to her working in front of you going forward. Same thing with ponying. Teach her to yield to the pony horse and follow the pressure of the lead, and you’ll soon be happily loping around the field.