I'm sad to say I don't. It was in a German-language interview and really stuck in my head. "Jeden Tag ein bisschen mehr Selbstdisziplin."

She wrote a memoir about her upbringing in East Prussia called "Kindheit in Ostpreussen." The English translation is entitled "Before the Storm: Memories of My Youth in Old Prussia." [1] It's a somewhat wandering story but the account of growing up in a Prussian aristocratic family on a huge estate is quite marvelous. That world--for better or worse--has perished almost without a trace.

[1] https://www.goodreads.com/book/show/138357.Before_The_Storm