That is your ideology being forced upon persons who desire death. There is no proof that people have free will and every death (suicide or death by cancer) is a natural death if free will doesn't exist.
> would it not be better to choose the 'death' the allows the person to continue to live?
That sounds like a worse fate if I was in the situation.
> It is nihilistic if you, and your coworker, believe that past a certain age threshold (or any other arbitrary measure) a disease/mental condition is untreatable and the best alternative is suicide.
That is just a forceful opinion upon labeling others and who just believe they should have will over their own death when the pain is unbearable. Her case is suffering from puberty and being conditioned throughout her life to be a certain way. She missed her youth, early adulthood and shouldn't be forced to live in today's society where she is constantly reminded of the abuse. She believes the best solution is suicide for herself. I only agree with her and think people should have authority over their own death after long talks with her.