Why is Saint Cecilia the patron saint of musicians and church music?

St Cecilia is the patron saint of music because as she was married, she (in her heart) sung to God, when she prayed to God, she could hear heavenly music and as she died, she sung to God.
The Acta of Cecilia includes the following: "While the profane music of her wedding was heard, Cecilia was singing in her heart a hymn of love for Jesus, her true spouse." It was this phrase that led to her association with music, singers, musicians, etc.