A harsher bit?

The problem with going to a harsher bit will be that eventually she will ignore that one as well. You have to keep working on her giving to the bit until she understands what you are wanting. Pull the rein to the right, as soon as she gives, even a minute amount drop the rein. Keep repeating this, she will give more and more each time. Then do the same steps to the left. She will learn that if she gives to the bit, you give her slack on the reins. It's a simple thing to fix, it just takes repetition and time.