"If I should not survive," she wrote, "how I die will show me who I really am."
Who she was is the subject of Susan Stein's one-woman show of a million emotions, now staged as part of the Live Arts Festival & Philly Fringe (livearts-fringe.org), with performances on Sept. 11, Sept. 12, Sept. 15 and Sept. 16 at Christ Church Neighborhood House in Center City.
But what eats at "Etty" -- and helps offer the complicated contour of the 29-year-old's life during the war -- is the dual role she played, in which her heart dueled with her soul.
To survive, the Nazis offered her their venal version of a Dutch treat -- serve on the overseer Jewish Council and, while assuring protection for her family, be complicit in the mistreatment of other Jews, deferring responsibility for their deportation to death camps.
What mattered most was not the incarceration at the camp but the incorrigibility of helping propel the Nazis' agenda through complicity. Could she survive the horrors ahead, or more, could she survive the shame and culpability of living while others died?
Survival, too, is at the root of what drove Stein on to consider writing this play, which is directed by Broadway standout Austin Pendleton: It was a car accident that nearly killed Stein and her children in 2006 which left her dealing with the bigger issues in life.
And nothing was bigger at the time than the lingering impact of reading Hillesum's diaries, which she had bought at a yard sale for half-a-buck years earlier.
It's not like Etty's complicated course in life -- with her one-on-one contretemps with God part of her diurnal yearning for understanding; an illicit relationship with her psychologist -- was on unfamiliar ground for the writer, grounded as she was in the horrors of the Holocaust.
"The project has been a perfect storm for me," says the first-time playwright, also a teacher at Princeton Day School.
If the diaries taught her anything, it is that "everything in life has led me to work on this."
Including her own history: "My great-grandmother was killed in Auschwitz. And when I did go there for research in 2007, I visited the Centre of Dialogue and Prayer," which offers seminars and workshops on the Holocaust, and is "run by a Jesuit priest."
Stein had a confession to make when he asked if she found Etty during her spiritual sojourn.
Ghost whisperer from the ghoulish annals of history? "I said I found my great-grandmother."
It was a find that would bind her to a personal legacy. "The project opened me up to understand my own past; it was Etty who opened me up."
And the author was open to collaboration; she found sources at such sites as the Etty Hillesum Research Centre of Ghent University. But her subject was also co-author.
"I focused on Etty the writer," rather than Etty on her eternal search for spirituality since the Holocaust victim was at once Jewish, yet "practiced Buddhism and read the Koran."
"At a certain point, I felt that I became Etty's writing collaborator, that we were in this together."
In a way, it was a theatrical threesome, with Stein stolid in her gratitude to Pendleton, for whom she had acted in an occasional theatrical role. "He said, 'No acting -- just talk!' " of his direct approach to her performance.
Did Stein ever feel that Etty was guiding her, sitting on her shoulder?
"I never felt her on my shoulder," she concedes. "I felt her inside my heart."