This is part of the reason why people keep talking about experience, and how you can't beat it with book learning, videos or chatting on a forum.
It's great that she is yielding to pressure, good start, and so needed, but it sounds like you have a respect issue going on. There are two sorts of yielding to pressure, there is the nice calm training one, increasing pressure and release, patience is key, waiting it out until you get that yield so you can release.
The other sort of pressure is when you are generally handling her, leading, tying her up, just generally being with her, if she invades your bubble at any of those times you do not need increasing pressure, you need a number 10 size meltdown. Now what that meltdown looks like depends on the horse. With my Emmy who is very sensitive, I just go 'momma bear' on her, turn full on facing, make myself as big as possible and literally growl out her while advancing, she pretty quick remembers her manners. Being she is low end of the pecking order she is usually very apologetic of making a mistake.
Big Bert was the other end of the scale, if she invaded I had to get after her physically, either with a crop, leadrope, hand, whatever, she was dominant mare, and I had to out mare her, the only way that she understood. She was not in the least apologetic, but she did remain respectful until the next challenge, but they became less and less as we worked with her.