For non-book readers:
Silverwing was once the mount of queen Alysanne Targaryen the wife of king King Jaehaerys I Targaryen, Vermithor’s original rider, who was also Silverwing’s mate.
While other dragons stayed in the dragon pit Silverwing and Vermithor stayed at the red keep. She took Alysanne to the Eyrie to see her granddaughters birth.
Silverwing was without a rider for nearly thirty years. As dragons go she is not as aggressive as Vermithor, perhaps because dragons take on traits from their riders Alysanne was a very kind and loving person.