In this quote, Annie describes her first experience of seeing a dead person. Since she didn't know this person, she feels confused and unsure about how to react. Because she lacks that personal connection, it's tough for her to understand or process what she's experiencing.
This moment also relates to Annie's relationship with her mother and the "small black ball." It shows how she's starting to feel more detached from her mother as she gets older, just like she couldn't connect with the dead person. The "small black ball" represents the heavy feelings she carries, like her confusion and sadness, and how she's drifting away from things she once felt close to. As Annie goes through different changes in her life, the "small black ball" grows bigger, showing how her emotions and the distance between her and her mother become even larger over time.