If you can, double lunge/long lining/ground driving....whatever you want to call it. I find that I have a much easier time getting bends and relaxation through the back and neck as opposed to lunging.

Or lunging in some type of side reins nice and loose encouraging her to stretch.

These are all coming from my english background, but you don't have to buy fancy stuff to do it. One lady I knew made her own "lunge aid" out of a long piece of rubber tubing. you connect it to the bit, then under the front legs and up around the withers, then under the other front leg and that side of bit. It was simple and worked without creating a lot of resistance and fussiness. Although I only saw it used twice by her in 3 months.