And then die. Don't forget the death part.
This is just classic, classic Child Star Meltdown. Kid gets real big real fast - the Hilary Machine basically only kicked into high gear 60 to 90 days ago, where she was suddenly EVERYWHERE - and it goes to her head, or at least her parents' heads. Suddenly they think the entire future of the company - in this case, Disney - rests on their child's shoulders, they suddenly make outrageous demands - and the company execs laugh their butts off, tell the kid to take a hike and find someone else. The kid's name is besmirched all over Hollywood, and it all goes downhill from there.
Plus, of course, 95% of all child stars lose their star power as soon as they hit adulthood anyway. Hilary Duff is very popular now, amongst a very narrowly-defined demographic: tween girls. That's the most fickle demo out there, and there is zero guarantee Duff can make the jump to adult stardom. Developing a bad rep in LA isn't going to make that any easier.