Hi. You didn't underline anything in the above text, but from the context of your question, we can understand that the "idiom" the question refers to is the expression "put her nose to the fire." In that case, I hope the answer below will help you.
Answer:
The expression "put her nose to the fire" means that Yoyo worked hard and dedicated himself to deliver the speech.
Step-by-step explanation:
As we can see in the text above, Yoyo was very dedicated to being able to speak at such an important assembly. In addition to creating the speech, he had to overcome the shame and stage fright and even the fear of expressing herself. But the text shows that she is a very dedicated girl who worked hard for this achievement. All this effort is represented by the expression "put her nose to the fire," which shows that Yoyo put herself in a situation that was uncomfortable for her, but that she was ready to face it.