Groundwork, herd hierarchy, pressure and release
This requires some vigorous groundwork to fix and can be fixed quickly.
You need to reinforce your dominance as herd leader. The herd is a hierarchical structure and the lower horses always listen to the higher horses. The higher horses determine and reinforce their dominance by getting the other horse to move their feet. Meaning that in any encounter between two horses, the horse that is forced to move is the lower horse.
Understandably, you want her to stop when you stop, but the reason she's pulling and ignoring you, is she is not fully regarding you as having a higher position.
To achieve this, it's important to make the horse yield to pressure. This is done during all our interactions with the horse. Not just while leading, but when in pasture with them.
This is a link (I move her backwards) and this link (in this part I move her sideways and backwards) to a parts of a video where I show how to push a horse back. This video shows (the first three minutes and it was a correction that was overdue) more aggressive pressure on horses in s herd that need to move. It's the middle of the night here, I'll create and upload a video demonstrating some of the techniques and link it in here.
To assist with leading, it's helpful to take the horse on chaotic walks, do not walk in a straight line and make it unclear where you are heading. Chop and change direction and if the horse pushes into you, use an elbow (gently) to push them away. If the elbow doesn't work, use the lead rope to force them to move out of your space, by twirling is in a circular motion. They don't like it.
I should add, as she is blind in the left eye, put your arm across in front of her chest when you stop, to help cue her. If she doesn't stop, correct her, a sharp tug on the lead rope should do it.
If a horse pushes on when I'm leading them, I will pull them up and make them do a circle, in a serious manner. They know when you are not happy with them and it is the same when a high horse corrects the infractions of a lower horse. Higher horses teach lower horses to listen to them. We must do the same. I've found that the best way to improve leading is to establish myself as herd leader within the herd and the leading isn't a problem.
There should be no need to use voice commands to stop the horse, the horse should learn to be respectful and stop when you stop, which is will if you have asserted yourself sufficiently and continue to do so. A horse that senses it can walk over a person, will.
Whatever training you do in the arena, also do it in the pasture with other horses.
From Horse and Hound:
Groundwork exercises to help with leading a horse
The first thing the horse needs to learn is how to yield to pressure,
one of those basic skills that should have been taught when he was
halter-broke, but, as Amy points out: “It is often a bit of a training
Push on any part of his body; as soon as he yields, stop pushing. With
your hand, you put a little pressure on his nose or his poll, and as
soon as he drops his head, release him.
Amy explains: “An easy, and important, one is to grab the top of the
lead nearest the head with one hand, thumb towards your horse’s chest,
and gradually apply pressure towards the chest until the nose drops
Once you’ve trained him to give his head, add a little more pressure
until he offers to back up, then release. Now you’ve trained him to
back, which is important for the next step.
Once he’s quickly and consistently yielding to pressure, it’s time to
take a walk.
“Decide how far behind you your horse should be and walk to that
distance ahead of him while he stands. Take a few steps with the horse
following behind you, then stop,” says Amy.
If the horse does not follow, put a little pressure on the rope until
he does, or if he sneaks up behind you, nearly crashes into you, or
tries walking past you, reverse him several steps, then ask him to
stand quietly for a minute.
The next few weeks of your life will be spent walking everywhere this
way: short bouts of forward, with corrections when the horse gets it
wrong. But soon enough he will be following at whatever distance you
decide, and you can practice varying the speed, using the same
techniques of stopping and backing to reinforce the idea of matching
Keep the lead rope slack
An important note - do not walk a horse on a tight lead rope. Allow plenty of slack, 2 to 4 foot for the horse, depending on the horse. A short tight lead rope puts pressure on the horse and if the pressure is never released the horse will not understand what it needs to do to remove the pressure.
The only time the lead rope should be taut is if the horse isn't following. As soon as the horse moves, release the pressure on rope to teach the horse, the thing you need to do to relieve the pressure is follow me.
A video by Rick Gore, I swear by his horsemanship.
How to lead a horse without a lead rope; Rick Gore Horsemanship; www.thinklikeahorse.org
Another great article:
A Pleasure to Lead