Hi! I can't tell you from experience as an adult, but I did have Fifth disease as a child. I do know a little about it though. Children are usually the ones that get it. There is not any treatment for it, you just have to rest and let it take its course. The only people that there is usually high risk possibilities for, are pregnant women and people who have really bad immune systems or disorders. If you do have an impaired immune system or some type of blood disorder than I would see a doctor to make sure you don't get any complications, but other than that it's just really an annoyance for several weeks. The good thing though, is that once you get it, you can never get it again. There are other conditions that can present itself like fifth disease, but if your niece had it, than I think it's a safe bet that it is, because it's contagious.