Serpentines. Transitions between gaits. Transitions within gaits. Lots of standing around.
It sounds like she needs to learn to relax, and I have an exercise I love for that, aside from the above. When working in the arena, or on a large circle, when she starts to speed up or gets chargy (is that even a word?), make the circle (or a circle) smaller and smaller until she slows down. Once she slows down, take her back out. I always start this exercise at the trot until they know what I want, then proceed to the lope. It's where I'm at with my little mare who's not real comfortable carrying a rider at the lope yet.