And now for something completely different, try Spontaneous by Aaron Starmer.
A darkly funny and spectacularly original exploration of friendship, goodbyes—and spontaneous combustion.

Mara Carlyle’s senior year is going as normally as could be expected, until—wa-bam!—fellow senior Katelyn Ogden explodes during third period pre-calc. ...
It was surprisingly good.

Another stand alone is The Doubt Factory by Paolo Bacigalupi (he has other excellent books: The Water Knife and Windup Girl are two more but they are not YA.)