Millet comes in two sizes. You may want to try the bigger (jumbo) sized millet.
In regards to treats, you want the reward to be *tiny*... such as a sunflower seed cut in half, or even quarters - if you can't make it into six pieces... so the idea of giving her an entire nut to crack open is rather too much!
You might want to consider buying a healthy nut mix that's already in slivers or crushed, and you can then make the pieces even tinier. The pasta may also work as well.
The reward doesn't have to be food related. It can also be praise, scritches, an item or even going somewhere! In fact, the higher the amount of reward items you have, the more it'll keep her interested in what she might get next!