Katie began following the controversial religion when she married renowned Scientologist Tom Cruise.
Now the pair have split, she has reportedly decided to return to her roots by rejoining a Catholic Church in New York .
But her actions may not be easily forgiven, according to childhood friends.
Kari Somo, a former classmate of Katie's at Catholic Notre Dame Academy, told Celebuzz those closest to the actress were upset by her decision to follow the church.
"We thought it was very shocking when [Katie] turned to Scientology, since we were all brought up Catholic, " she said.
"I know [Katie's] parents had an issue with it. I don't think they were very happy with it.
"[It was] jarring — and caused severe rifts within her family."
Another former high school buddy, Angela Domschot, says Katie turned to Scientology out of love for Tom.
"We were all shocked when she turned to Scientology but when you're besotted with someone, I guess you'll do what they want," she said.
According to the report, Katie was the epitomy of innocence at high school: the article reveals she didn't even have a boyfriend at school because her parents' strict Catholic principles discouraged it.
Since filing for divorce from Tom last month, Katie has reportedly gone to huge lengths to stop the couple's daughter Suri being influenced by Scientology .
According to reports, she recently enrolled the six-year-old at New York all-girls Catholic school, Convent of the Sacred Heart.
Meanwhile, 'experts' are already predicting that the next Mrs Tom Cruise will be a devout Scientologist.
A former member of the church claims Latin actress and 'Scientology princess' Yolanda Pecoraro is perfect for Tom.
According to the National Enquirer, the two met at the opening of a Scientology center in Spain in 2004 where Tom 'fell head over heels' for her.
27-year-old Yolanda, who has been studying the religion since she was 13, told the Enquirer: "Yes, I knew and still know Tom Cruise. And no, I'm not married and engaged."
Scientology expert Margery Wakefield encouraged speculation about the could-be couple, saying "Tom's next marriage will be inside the church".