The London-based clothing designer wrote how her studies were, "the missing piece. Suddenly everything began to make sense.
"I became that annoying girl in The Org who would just talk endlessly about how incredible training is and how phenomenal the internship is. I'm sure a few people couldn't deal just like I couldn't. But I won't stop with that because now I KNOW," she continued in the lengthy letter.
She then went on to encourage her fellow Scientologists to start the mysterious organisation's auditing internship.
"We all need to do this. It’s hard work. It’s a lot of effort. It’s a few melt downs and running to the bathroom to have a mini episode, but it is worth everything because you will get through. This is a gift to yourself and so many others
"The internship, for me, is what made me a Scientologist... Thank you to my Dad for everything."
There was no direct mention of her adoptive mother, Nicole Kidman, however she did write that "It took a whole family" to get her to the level of "auditor" within the religion.