What are you doing differently? Sounds like you are not giving with the off hand.
Pick up the reins--slide the hand on the side you want the flexion down the rein and then pull with that hand while giving with the other.
Remember when she gives release like RIGHT NOW!! It does feel different because of the weight of the other rein.
Give with the off rein and release as soon as she gives. Build until she will touch her belley and break at the poll AND KEEP HER HEAD THERE UNTIL YOU CUE HER TO PUT IT BACK--by pulling on the off rein.