There are two reasons why you want ground manners: One, you want to be an effective leader and gain respect from your horse. Two, you want to use this stage to develop transitional cues to help with your introduction to saddle work in the near future. In order to gain respect, you need to gain control of your horse’s feet. That is the short answer to the first part of your question, “…what do I do?” If you get control of her feet, you automatically establish yourself as the leader and achieve respect from your horse.
In answer to the second part of your question, “…how do I teach her good ground manners?” you will need to learn and execute techniques on how to gain control of your horse’s feet. There are a variety of detailed exercises and maneuvers you can use to achieve this. You also will need to know how she thinks and you will need to think like her. It is critical that you define your view of what acceptable ground manners are and establish a daily lesson plan on how to achieve those acceptable ground manners. Before a person begins training of any kind, they need to define the objective. Clear communication is a basic component of any training program.
“Horse’s thinking” Most horses think the same regardless of their age. Your mare was born with good ground manners. At birth, horses have all their instinctive behaviors and are fully developed (precocial) and are fully physical and ready to learn neurotically. If the baby gets out of line, the mother or the herd will put her back in line. But, she does not know what you know, nor does she know what is right or wrong in your world. The problem you have is that your concept of good ground manners is different than her concept of good ground manners. As an example, in many lands it is customary to belch at the dinner table following a meal to show your satisfaction of the meal; however, to most people in western society this is rude behavior. Likewise, when a horse pushes you out of the way or steps on your foot, they are being horses and showing leadership by controlling your feet. Remember this - leadership is a fundamental behavior in horses, and it requires a leader and a subordinate. In their world, the one standing is the leader and the one moving is the subordinate.
Teaching your mare what is acceptable in human society is all about how to control their feet. Your job is to outthink her. She can outweigh you by 4-5 times in her weight and size, so you cannot physically show her what is acceptable. The simple concept to gain a horse’s respect is to not only move their feet but to have control over their feet at will. To simplify this, break the horse up into five body parts (head, neck, shoulders, ribs, hips) then work out of a round pen or on a leadline. Many people start using the round pen to get the horse moving forward at liberty and for getting inside and outside turns. If you are working off of a leadline, find a starting point such as disengaging the hips around the forehand without the horse moving forward. Once you can do this on both sides, start working on moving the shoulders around the hunches. Forward impulsion comes from the hips and turning comes from the shoulders. Once you have gained control of hips and shoulders you now have control of impulsion and turning. This is just a basic overview of what is required to gain respect from your horse - one of the key elements in teaching good ground manners. Now, you are ready to buy videos to watch and/or books to read to see exactly how to get the different body parts to move correctly and softly without getting into a fight with your horse.