My two year old filly is very easy to handle and to work with. Until you try to take the other horse out of the pasture. As soon as I open the gate she is barging her way through. I have tried many different things and obviously none of them have worked. Can anyone suggest something. This is really starting to tick me off!!
The root of this problem, and almost all bad ground habits is lack of respect for you. You are a "flea on the butt of an elephant" to her. I'll bet she also steps on you when you lead her. I can guarantee, if the boss mare was standing in the gate, that filly would never charge the gate. Why? Because she'd get the begeebers kicked out of her. The boss mare has an acceptable amount of "space" around her that is not encroached upon. You need to recapture that "space" for yourself.
If you're not comfortable, scared, not strong enough or not quick enough, take the horse to a trainer. You'll end up with a well adjusted, safe member of the family, that understands her place. If you fail in your training, the horse gets worse and will take harsher techniques to cure.
Put a halter on her with a chain over the nose. Open the gate, but don't stand in front of her. When she charges, yell whoa and snap the chain as hard as required to get her attention. Make her stand still and repeat, allowing her to only take a step at a time. Pretty soon she won't move until you tell her to and she'll be tip-toeing out of the pasture. This is the first step. Now that you have her attention and she is gaining respect for you, go to the next step - carry a big stick. Put her in a round pen and get her trotting or loping. Stand in front of her with a whip and snap it, yell, wave your hands, etc. to get her to go around. This is dangerous. It's a game of chicken. A really aggressive horse will run you over. The horse has to understand that you have an invisible "space" around you that cannot be invaded, for any reason, at any time, no excuses. When leading her, carry a crop and poke her in the shoulder, or in extreme cases, hit her if she enters your "space." My "space" is arm's length. I don't ever want to have a horse closer than reaching out and touching them with a straight arm. Any more and it's hard to lead them. Any less and they walk on you. Don't make allowances or excuses. If a purple alien with sparks shooting out of it's eyes, lands on the horse's back, grabs both ears and ties them in a knot, that horse had better find another place to go other than my "space."
Now back to the pasture, carry the crop or whip with you. Many horses start crowding the gate before it's opened. Before you open the gate make sure the horse is giving you room. Open the gate, blocking it with your body, and make menacing gestures and snap the whip. Do it before they ever get near the gate. If you've done your homework, the filly won't dare run you over. If she does, go back to leading and the roundpen and start over.
These methods may seem harsh, but a horse that runs over you is dangerous. If you think this is bad, watch a boss mare kick the begeebers out of a smart-alec two year old. Once again, get a triner if you're not comfortable with any step. My wife handles all our young horses, until they begin their terrible twos. When they get her number, she hands them over to me to teach manners. All her years around horses and she still can't handle a horse that steps on her.
I want to be able to sit on a horse, turn around and talk to someone behind or to the side, trim a branch off the trail, or get a beer out of the pack, without the horse taking off. As long as my reins are dropped, I don't want them moving. Once I pick up the reins, they should know it's time to get busy. Is the mare extremely sensitive to leg and seat cues? Maybe she is just trying to please, thinking that everytime you move, you want to do something and go somewhere. If that is the case, you need to desensitize her. Aim her into a corner of the riding arena, drop the reins but keep hold of them, and brush your legs on her side and shift your weight. When she moves, she'll try to get out of the corner. Insead of bumping her in the mouth, steer her back into the corner. Pretty soon she'll understand that unless you pick up a rein, you don't want to go anywhere. Once she'll stand still in a corner, with you moving and bumping her side with your legs, begin picking up the reins and asking her to move. Then put her back in the corner, drop the reins and bump her with your legs. Pretty soon she will realize the difference between incidental contact and picking up the reins to work. Once she has that, move away from the corner a little at a time, until she'll stand anywhere unless you pick up the reins. Susan is right. Not much you can do for a year or so. Stopping while leading is a problem. I never belive people that say their horse is halter broke until I lead them myself. I can just hear the horses in the pasture talking about how they their human is halter broke. "You know I can go wherever I want to go, stop whenever I want to stop, jump on top of them if I act real scared, dance around when they want to stop and all the time they're fedding me treats and telling me what a good boy I am." I don't consider a horse halter broke until they: walk quietly at my shoulder, without any pulling on the halter; stop when I stop, without touching the halter; trot out at my shoulder, without pulling on the halter; walk through a puddle, even if I'm walking on dry ground, without stepping all over me; and stop and stand quietly whenever I want to stop. If you ever have to stop and wait until a horse decides to walk off, and tug on the lead, I don't consider them halter broke. I love to see a real horseman leading a stallion through a crowded horseshow, and the stallion is leading quietly, completely attentive to his surroundings, but knowing that he'd better not whimper or break his stride. That's a halter broke horse. Work on him doing exactly what you want him to do, when you want him to do it, not when he decides to. Just remember to keep the lessons short, praise only if he truly does something right, and heap on the praise if it's deserved.