It's tempting to give in depth explanations because she is so intelligent and has displayed that she is aware of these very complex issues.
But my advice is be as age appropriate as you can. Don't brush off her questions, because her concern will probably grow if she senses these questions are "off limits", but keep it sweet and simple if possible.
I think the best way to handle is: Unfortunately, honey, sometimes this happens to some people, but it will never happen to you.
There are very intelligent adults who are working very, very hard to solve these problems.
Off the top of my head that's the best I can come up with.
Gotta run to school, but will check back in later. Hopefully you'll have the problem solved by then!