I think you need to change your body position during your pivot. Don't pull her forward before you push her into a pivot. Instead pull her forward during the pivot.
To start the pivot, you should turn your shoulders to face her head and walk into her space. I use a smooch for my pivot cue, so just as I turn to face my horse I'll smooch & then take that first step. During the pivot, I will increase or decrease the size of my circle to help the horse hold her foot in place. If your horse is in-tune enough, all you should really need to do is move your hand on the lead chain either forward or back.
In your case, you'd want to concentrate on making your circle just a tad bit bigger. Be careful that your hips/shoulders aren't turned towards your horse's body. You want to open up some space so your horse has room to come forward. If your body is turned towards the horse's, you've effectively closed the door & your horse has no where to go. Also, take it slow. If you watch your horse's body position - not just that pivot foot - you'll know when you need to bring her forward. Start by moving your hand forward & if that doesn't work, really open up your circle.
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