Before sidepassing from the saddle, she needs to know how to sidepass from the ground. To sidepass, she needs to know how to move her shoulders and also how to move her hips away from pressure. Initially when you start teaching a horse you would focus on direct pressure on their shoulder to move the shoulder and direct pressure on the hip to move the hip. The sidepass puts those two cues together - one step over with the shoulders followed by one step over with the hips. Done simultaneously, you have a horse who can sidepass.
So when you are in the saddle, she needs be able to move her shoulders and her hips individually. Can she pivot on her haunches? Can she pivot on her forehand? If you don't have these skills yet, you aren't ready for sidepassing. Your leg cue at the girth moves her shoulders over for the pivot on the haunches. Your leg cue moved farther back, almost near her flank, moves her hips over to pivot on the forehand. One end at a time, one step at a time - shoulders, then hips, shoulders, then hips - will get her to sidepass. You leg cue somewhere in the middle of the individual cues to move her shoulders and her hips will eventually be the spot to cue for her to sidepass.
If you want her to spin for reining, you need to concentrate on getting her to pivot on her haunches while keeping forward momentum. Work on your pivots in small increments...a quarter of a circle at a time to start with. Then walk out of the pivot to help her keep the thought of going forward in her head. When you get better and better at this, you can increase the size of the circle (pivot) to 1/2 circle and trot her out of the pivot. Mix it up a little bit to avoid boredom.
Perfect Jin N Scotch - 2004 APHA Palomino Overo Gelding - Western Pleasure and Showmanship
Hanks Rainy Sky - 1998 Black and White Tobiano Paint Gelding - relaxing rides and blazing trails