Answer:
Expound can mean she has to further do an in depth explanation of the topic.
Explanation:
When she gave the lecture, and according to her preparation, she did what she was planning on doing and achieved her plan. But, when she realized that the students are still confused and seem to be lost and unable to grasp the whole lecture, she felt she needed to give a detailed explanation of the same lecture, but this time in a much easier, more detailed lecture, for them to fully understand it.
