Question

why might someone be gleeful?
because she has just heard some good news
because she is nervous about an upcoming test

Explanation:

"Gleeful" means feeling great joy or delight. Hearing good news is a common trigger for such positive emotions. Being nervous about a test is associated with anxiety or worry, not gleeful feelings. So the first option is the correct reason for being gleeful.

Answer:

because she has just heard some good news