Diagnosis of Nicole...not just a rich brat
Okay, so let's review the facts;
Nicole's mother committed suicide; result of depression
Nicole saw this; trauma, possible PTSD?
Nicole is impulsive; possible ADHD?
Nicole has severe mood swings; possible mood disorder
Nicole abuses substances; potentially self-medicating? Or possibly just normal teenage rebellion, of course.
Nicole doesn't need much sleep; possible manic state
Nicole doesn't need much food; another manic sign
Nicole experiences extreme depression; possible major depressive disorder
However...combine all of these and you get a classic case of Bipolar disorder! If you consider all of these things and take her actions into account...it is a classic film depiction of bipolar disorder with both manic and depressive episodes. Additionally, 10-15% of all people who have a bipolar mood disorder succeed in committing suicide during their depressed episode(Nicole's Mom).
This breakdown clearly shows that she was NOT just a spoiled, annoying, little brat who got everything she wanted. And her daddy didn't cause it by being absent or letting her get away with things or any of that. With treatment (medication and psychotherapy) her episodes could become less intense or even manageable. They tried several times to get her help, and if she had let them it might have gotten much better for her.
There was a VERY similar film made in the early 90's with Drew Barrymore and Chris O'Donnell, Mad Love. Another great watch to explore bipolar symptoms and activities. Mr. Jones, with Richard Gere, is another great watch on bipolar disorder, but he is not a teen in the film.