Okay, I would suggest flexing in the bridle and one rein stops next. Then you could try bending at the walk. You flex her head while rolling your heel or spur on her ribcage. Same side. When she softens to the bit release your arm down to your knee. If she tries to straighten out pull the rein back to your hip. When she is soft release your foot and the rein and let her walk straight for about 20ft then pick up again. Eventually she should keep slack in the rein after you release and cross her hind leg as she circles around your leg.
Here is a video of my horse rogue flexing and doing one rein stops. She is a little rusty and wasn't rating my seat, but it should give you a good idea what you are looking for. Right before you ask her to stop sit down and relax. Give her a chance to stop. (count to 2) After a while she will realize that after you sit you are going to stop. In the beginning the faster you are going the stiffer she will be. I didn't do many stops at the walk because Rogue knows what to do. I flex her everyday when I get on. Also I usually don't steer when doing the one rein stops. (I was trying to keep her away from the camera person today.
) I also bumped on the rein when she was leaning on the bit. (Again because she knows better.)
Hope this helps.