LONDON — By the time she was 17, the Dutch teenager had written a harrowing memoir recounting repeated sexual assaults and her subsequent experience with post-traumatic stress disorder, depression and anorexia. Last year, when she was 16, she approached an end-of-life clinic in the Netherlands seeking euthanasia or assisted suicide, but was rejected because her parents had been unaware of her request and she needed their permission, according to a local newspaper profile published in December. When her sister announced that the teenager, Noa Pothoven, had died at 17 early Sunday morning — without revealing where or how — the...