I have tried introducing side reins on her before, and I took the advice of keeping them very long to being with. I worked up to tightening the reins just enough so that there was a light contact with her mouth when her head was at rest (still fairly long).
What I am seeing is that she does not want to work into the bit. She does not want to keep a steady contact with the reins and will overcurl in order to keep the reins loose. It is much more difficult to get her moving from her hind end on the lunge since I do not have my leg and seat aids. My attempts to push her forward into the bit only result in her speeding up rather than pushing through.
I don't want to crank her neck in just to achieve this contact as it will not be a true contact and will do nothing for her topline. But I am not very good with lunging (and neither is my horse) to begin with and need some guidance.