Katy Perry was greatly influenced by gospel music. She sang in her parents church (both are preachers!) between the ages of 9 and 17. As you figure out Katy grew up listening to gospel music. Her conservative parents forbade her to listen to mainstream pop music. (Perry's mother called pop music "secular music").-->
When she was a child, Perry attended Christian schools and camps.
As a teenager (at 15), Katy's singing in church attracted the attention of rock veterans from Nashville, Tennessee, and as a result Katy pursued a career in gospel music under her birth name (Katheryn Elizabeth Hudson).
Perry signed to the Christian music label "Red Hill", under which she recorded her first album at the age of 15. Performing as Katy Hudson, she released a self-titled gospel rock album in 2001.
Katy supported this album with "The Strangely Normal Tour", accompanied by Phil Joel, LaRue, Luna Halo, Earthsuit and V*Enna. The album was unsuccessful as the label ceased operations at the end of 2001. In 2007 Katy signed with Capitol Records and changed her surname to Perry, her mother's maiden name, because "Katy Hudson" was too close to movie actress Kate
Needless to say that growing up listening to mostly gospel music, Perry had few references when she started recording songs. When the producer asked her with whom she would like to collaborate, Perry had no idea.
Perry has admitted that her perspective in music was "a bit enclosed and very strict" and everything she did was church-related.
Katy told Blender Magazine that during her adolescence, she wasn’t "your typical Christian. I’ve done a lot of bad things. Use your imagination."
On the other hand, Perry revealed to the Rolling Stone magazine: "God is very much still a part of my life. But the way the details are told in the Bible - that’s very fuzzy for me. And I want to throw up when I saw that. But that’s the truth... I still believe that Jesus is the son of God. But I also believe in extraterrestrials, and that there are people sent from God to be messengers, and all sorts of crazy stuff".
Unfortunately, the Christian community didn't take well Katy Perry's decision to abandon her gospel career and become a famous pop star wearing all those sexy outfits and underwear, not to mention posing naked...
Conclusion: Just because Katy Perry has turned into another music genre, that doesn't mean she doesn't beleive in God.