Laurie Halse Anderson writes YA and youth fiction about hard-hitting issues. She is celebrated for her ability to face sensitive topics head-on without sounding preachy, didactic, or awkward. She accomplishes this real, honest voice by responding to every single message she gets from a teen (email, letter, whatever) and listening to what they tell her.
Speak (1999) (which you may recognize from the Kristen Stewart movie if not from the book) touches on several difficult topics, but centrally, rape. Wintergirls (2009) focuses on anorexia nervosa and bulimia. Even in her books that aren't problem novels, like her historical fiction novel Fever 1793 (2000) the protagonist has to deal with death and other issues.
This week's review book, The Impossible Knife of Memory (2014), deals with a parent who has post-traumatic stress disorder.