http://www.vanderbilt.edu/htdo.../MUSL242/cecilia.htm
It is not until late in the fifteenth century that Cecilia quite suddenly began to be associated with music. She was declared the patron saint of church music by several musicians' guilds and began being regularly portrayed playing the organ.
Along with St. Catherine, St. Cecilia is considered one of the muses of poetic art. This fact helps to explain why she so often appears in art. Another reason St. Cecilia appears widely in art is because artists like to work with the "rapt expression" associated with St. Cecilia's facial expressions (Jameson 345).
Thank you again Teo for this interesting topic.