Skyseternalangel has made some great observations, particularly on how your body language is confusing your horse while lunging. A couple of my own thoughts:
I will make it a permanent habit now to have my chest face her HQ and stand further back to the back half of her body vs dead centre towards the barrel. This should prevent 100% from me untentionally getting near her shoulder area.
Yes, backing is an excellent response to some behaviors, and you don't seem to do much of it. That would be a good thing to work on. One step, then two, but ultimately you should be able to jog forward and your horse should be backing away in a straight line fast enough to keep pace.
I have done a lot of backing with her but first she hates it and actually brings out the worst in her cause she is very resistant in backing. Past trainers noticed this when working with her and said to only back her when needed and NOT as a correction. They said they dont want her to see backing as a correction cause in the saddle, she was taught backing as a good thing and was rewarded so if you back her all the time when correcting, when she gets back in the saddle she will be confused.
So backing her only when i absolutely have to has been an adjustment ive made over the past couple months.
Backing her normally is great, she backs up every time with barely any pressure. If im backing her with her on my side, all I do is put my hand on the snap and she starts to move back. If she doesnt, then i just move the snap back a bit with no pressure in the lead and shes already moving back.
Its when you move her back aggresively, 10-20ft with constant in her face pressure that really agitates her. She will resist and try to bite even if you try to back her 20 ft from putting back pressure on the snap, she will physically curl her head downwards to block you from getting a hold of the snap.
Past trainer quickly saw this and insisted I do not do excessive backing with her and especially not aggresive backing. They said backing her for any distance greater than 3 or 4 steps is pointless, serves no purpose and will only get you an angry irritated horse.
You mentioned that your horse doesn't like being asked to move away from you when you turn into her. On this little rodeo that starts at 3:59, the two of you get in a squabble about it. Maybe all you needed to do was give her a sharp elbow or a whack with the flat of your hand THE SECOND SHE DIDN"T GET OUT OF YOUR WAY.
I gave her a quick elbow, not hard but enough to tell her to get over. She took offense to it.
Also, is the far right of the screen the way back to her stall?
No, where the camera was is the way back to her pasture paddock.
It's fine to hit your horse when hitting is appropriate. It's never OK to get mad.
I didnt get mad, I got firm. I never yell, my volume in my voice will come up when i get firm though but not to the point of yelling. I wanted to get big and my voice helps.
Have your answers ahead of time so you work through the issues without losing your cool.
I dont think i was losing my cool. I know its hard to describe, but because I learn a lot and pick up a lot from watching and observing my past trainers and my current one and how they work with horses and my own. Ive been working to follow their leads, everything in terms of body language to how they firm they get on the lunge line, etc.
When I first started I was as soft as butter when lunging. I couldnt get her to even go anywhere on the line. Trainer basically put it, she isnt taking me seriously because im not firm and assertive enough. She would always be able to change directions and choose which way she wanted to go and i wasnt able to stop or prevent her. Now, thanks to previous trainer who taught me how to be much more assertive, (and you can see a couple times in the video where she tried to change direction), Im able to get her to stop right away and go the direction i want her to go. Being a lot firmer with the lead and my body language was the biggest factor. Before I was way too casual, my tone of voice was too light and when I needed to up things, I didnt up them enough.
Two of my past trainers (one was a Parreli trainer) are very hard on their horses when correcting. If you think Im losing my cool in my video (again im not), then you wouldnt want to see my past trainers. They didnt lose their cool but they got big and firm in body language and tone of voice. I learned a lot from observing how they handle horses. They may have been hard when needed but it only made the horse better,
One other thing. You might want to try putting a piece of duct tape on your lead rope, at least three feet from the snap, and practice not putting your hand past the tape. You are sort of choking up on the lead, especially when you turn, and micromanaging your horse's head. Just leave the rope slack and make your turn and expect the horse to follow you. If she doesn't, you can fix it then.
Current trainer wants me to hold her lead 8-12" from the snap and no longer.
This was perhaps the very first adjustment she got me to do. I used to always lead her with 2ft slack in the lead (which my past trainer made me do).
When I first started leading (not with her at this time), I led with 8-12" slack from the snap, just enough slack for them to lower their head (not to the ground but enough).
Then previous trainer said to allow a lot more slack in the lead so I adjusted to having 2ft slack to the snap. This carried on for 3 months.
Now my current trainer wanted me to go back to how i was doing it before.
See, this is the effects of having switch trainers so many times (untintentionally of course). Every trainer has their own preferences, I get told one thing by one, then something entirely different by the other. But now that I have one trainer and only one trainer to work with for now on, it really helps sticking with one mindset and teaching method.