When Emily quotes writer Dudley Clendinon, an ALS patient, as he describes his first-hand experience of the disease, she's relying on what kind of source?

She is relying on the primary source. This is because, the writer is first hand information about the experience of the author. What made it a primary source is also coupled with the fact that, the writer is the one that experience it and the one that is wrote the book based on his experience.