This young girl was "running to rejoin her family members when she collapsed." She had just exited from a ride (unknown at this point), and her family witnessed her demise.
As for pre-existing conditions: I suffer from extreme high blood pressure and epilepsy. I used to be a 'daredevil' and defeat many rides' safety devises for a more 'thrilling' experience. I no longer take risks with my own life and (nearing 50 years of age) I no longer ride mechanical thrill rides. If something were to happen to me on an attraction, not only could I end up dead, my family would grieve, and my passing would disrupt the lives of many others.
That all being said, would this be in the news if it happened at... say a restaurant or a minature golf course? I hate to say it, but the theme park death story is getting to be old. I have a question. How many deaths were there last year, or how about each year for the last ten years. Does anyone have those statistics. I imagine that if we can find those numbers, we would probably find that the numbers are similar, and that this ongoing story is another example of the media taking a story and running with it. It is important to check yourself and make sure you are fit to ride, but don't let this be another media scare story. (I won't get on that soapbox..at least not yet anyway) Know your limitations, but go to the park and still have fun.
As for this little girl, I really feel sorry for her. I don't want to imagine what that'd be like to see your daughter just collapse and die in front of you. Nobody should ever see their children die before them, ever.
That aside, however, this cannot be blamed on the park, or its staff. I'm not a huge Six Flags fan, but I know they wouldn't wish this to happen.
A 10 year old child's body is no where near fully developed. Not to mention handling the forces and stress a ride or attraction may have.