If your horse keeps trying to stop and turn in to look at you, that means that YOU have positioned yourself too far forward in relation to her body. When you want the horse to go forward (let's say in a clockwise circle to the right), then you need to "point" with your right arm, and make sure your shoulders are also slanted to the right, and that your body position is at her hip. The entire time she is going, you need to keep that position at her hip.
When you want her to stop or change directions, then drop your "pointing" arm, face your shoulders to her, and position your body so you are ahead of her shoulders. (essentially cutting her off)
All of this is very hard to explain over the internet. It's much easier to have someone show you in person.
But it sounds like to me you are not lunging her correctly, and you are confusing her.
with regard to the bolded portion:
unfortunately, this is often the exact opposite of what is happening when a horse will repeatedly swing it's hiney out and face the handler; it's not that the handle is too far forward, but that she is too focussed on the hors'es hind quarters, thus driving them away, leaving the head looking inward.
Kind of think of the horse as a toy boat on a pond. it is long and relatively straight, with a front and an end. If you were to blow on the hind half of the boat, it would move away from you, leaving the prow facing you. If you blow on the front, from a side angle, it will move out away from you. If you get in front , or at an angle that is too much from the front, and blow, the boat will slow down and maybe go backwards.
Now, a horse is not a boat in that it has a mind, and you will really move the horse by moving it's mind, but if you think of yourself as "blowing" the horse forward, as if it had sails, this can help you. You apply the "blow" , or the Pressure, right at where the girth would be, or better to imagina, where your own leg would rest if you were riding. Why does the hrose not just move sideways away from you? as a boat would? Becuase you use the lunge line to suggest to him/her to make his movement FOREWARD instead of sideways. That line is your "rein" and you use it to get the horse thinking "forward". But, if you try to chase him forward by putting a lot of pressure on his hip, he may likely swing that hip away from you in a defensive manner. You can still be successful applying presssure at the hip, IF your directing with your leading hand (which uses a bit of a tug in the direction you wish the hrose to go to get him moving forward in that direction) is strong enough to change the hrose's mind from a "I will flee sideways" to "oh, she wants me to go forward".
If you put pressure way forward of the cinch area, the horse will swing his head/shoulders away from you; something you would want to do if the hrose had swung in to face you.
But, if the horse has swung in so that she is now perpendicular to the circle and directly facing you, you have to get access to her shoulder to move her out, right? her inside shoulder. To do that, you actually move her FACE over and out of your way, in the direction you want her to continue circling.
I will use the leading hand to put some pull leftward (say we are lunging counter clockwise, so horse goes off to YOUR left),. I use the turn of my shoulders and body language that the others talk about, and pointing with the leading hand, and if necessary, some tugs on the line. Then, I will literally walk toward the horse, slowly, putting some pressure on his INSIDE NOSTRIL. by pressure, I mean i kind of tap tap the air, as if I were tapping on his face. I walk closer and clsoer. If he doesnt' get the idea, I will literally run into his cheek area with my tapping fingers and keep it up until he steps sideways , away from me, and out onto the circle. Once he does that, I use the tug of the line to indicate "forward, leftward" and put some driving pressure on the girth area, which, since the hrose has stepped away from me, is now available to me.