It seems to me that you are complicating
things too much and over thinking everything. Things are much simpler once a
person is aware of what is going on. In your case and situation the strong nudge
you got from the mare simply means "let's go home, stop it!". In short, the
strong nudge of the head against your body is simply a request, hence many do it
when being fed out of hand and such, or when stopped and want to proceed. It is
disrespectful to say the least, not something that speaks highly of the handler.
Remember, just like among people, one cannot demand respect, one has to earn it, and that not by kindness, treats or petting the animal, but simply by responding to the animal not only suitably and with speed, but mainly with the consideration of the animals concerns and well-being, physical and mental alike! You could say that a horseman has lively spirit, calm mind, brave heart and strong but sensitive hands.
I cannot comment on what is going on because I have to at least see it in order to become aware of what is going on. You are describing what you think is happening and not what is actually happening, which is self-evident in your writing. In any case, you need to simplify things and not complicate them as you are doing. I have also said in the entrapment article that using the prolonged way requires more expertise, hence in most cases people just snap the girth (surcingle to be exact) on semi-tight and let the horse buck itself out, and then they tighten it. Once the horse is accustomed to the girth/surcingle they do the same with the saddle.
It is much safer to have the horse adjusted to the tightening of the girth before using the saddle, lest the horse jumps, bucks or takes off during the tightening process of the saddle, which could result in the saddle turning under the horse and such damages are often permanent, since the first experience with the saddle was so dramatic for the horse, especially if the saddle slides back and under and the girth ends up in the flanks as if some bucking strap.
In some cases people put just the girth/surcingle (no saddle) on the horse in the stall, and turn the animal lose, then when the animal stops bucking or jumping around they tighten it again and leave the girth on overnight. Walking the horse around with the saddle on top and with a lose girth is 100% NO-NO! The horse should be accustomed to tightening up the girth at least enough so when doing it with the saddle we do not surprise the horse during the tightening process and horse gets away from us when the saddle is not tight enough to be held in place.
The way you are doing it is a good way to mess the horse up, and I did come across a horse that was messed up in similar way (much worse though than your case), when the person did not tightened the girth enough and as the horse jumped the saddle turned around and ended up under the belly of the horse. To add to this problem the girl then sent the horse to some "expert" trainer who ended up doing the same thing but this time with a western saddle. The horse was ruined for life in this way and never fully accepted the girth again.
You should teach your horse to longe (running free in the pen is not the same thing), tighten the saddle fully and then longe the horse. It is normal for the green horse to jump or buck; hence we keep moving the horse forward during this behavior via the longe whip, while slowing it down if the animal wants to run too fast. We do this in both directions. The longe line is important in controlling the animal as well as calming it down, but one has to know what he is doing. It is recommended that when using a saddle for the first time we use English saddle rather than Western, and without stirrups. Not only that such saddle is lighter but also we do not add unnecessary stress on the horse via the stirrups bouncing against the horse when moving.
I personally prefer to start horses with English saddle and once the horse is started I use the Western saddle if required. One cannot truly ride the horse in a Western saddle, since that saddle is made more or less for travel or work, and not for training horses. There are some horses that have problems accepting the girth/saddle, but most of them can be worked with by longing them first before mounting.
I have also said in the article that doing it the slow way is also more risky as one with less experience is more likely to mess the horse up. If you make a problem of something simple, it will become a problem to the horse and the animal will respond accordingly as to a problem. The horse flipped because you have mismanaged the situation and your responses were too slow and more likely unsuitable, hence the result. In short, things with horses are very simple but not easy. In most cases amateurs reverse this concept thinking that things are easy enough that they can manage them, and then they end up over thinking the simple things and complicate a hell out of them, which seems to be apparent from your email.
If you have a chance make a video of what you are doing and send it to me and I will comment on it. Please keep in mind that if I find my replies useful to other people I will publish them on my site, lest someone else will ask the same question. I will also use the video publically as well, but names or locations will never be revealed.
In conclusion, and in addition to the above, many horses that are just being broke and ridden in the saddle tend to developed muscle soreness under the girth (often caused by excessive longing with the saddle/surcingle or riding in a circle/pen), which often produces some swelling (it's hard not soft and to a greenhorn it could look like part of the muscle) usually in front of the low girth area on both sides, one side usually more sore than another, hence horses often respond unpredictably when turning (stepping/extending to one side). The sore muscles may or may not be sore to the touch, but once the girth is tightened it can cause a sudden pain during particular movement, like turning, and the horse responds accordingly.
Starting young horses should be left to people that already have some experience in doing it. There are so many horses messed up just because the amateur or unqualified person thought that it was easy enough that he could manage (the fool usually sees it as some challenge). And as you've already learned, once the horse is messed up it is very difficult if not impossible to correct it, since nothing the animal learned will ever leave the "instinctive tree".
Of course there are horses that will never fully accept the girth, or the bit, or the rider, or the legs, no matter what one does, and such horses are simply unsuitable for riding and are best of being destroyed, lest some fool breeds these animals and procreates these deficiencies.
Sorry I could not be of more help.
I have said that there are horses that will never fully accept the girth/saddle. I had a few of those, and they may go just fine for a few days, even weeks, and then out of nowhere they just "blow up" (buck, rear, spin or what not). In such cases one is better off getting rid of such horses and gets a new one. Consider the unnecessary danger that you are exposing yourself to. I have witness many serious injuries to people (mainly women) caused just by such horses, because those folks were too emotionally involved with the animal and could not dispose of it, and kept on trying to correct/fix something that could not be fixed/corrected, believing that it could be corrected with "love, kindness and patience". (Most greenhorns and amateurs will hide behind those words whenever they are failing in training of a horse.) In all these cases I have advised those unfortunate to get rid of those horses, and only a few listened.
We used to have a saying that if a horse does not accept the bit within two weeks he will never accept it, and the same goes for the saddle. Most normal horses, when done properly, accept the bit and the saddle within two to three days, providing one works the horse every day.
There is a difference between courage and foolishness, as well as, between quitting and just letting go.
Written by Ludvik K Stanek a.k.a Lee Stanek