The girl seems to have a good understanding of dose safety. But a poor understanding of biological effects, just like everyone else. Beta vs alpha vs gamma radiation have very different biological effects and sieverts, the measuring units that take some of these differences into account, are a gross over simplification. You can kill someone with a radiation dose well below the lethal one in Sv and you can survive a dose above the lethal one...
Biological systems have very complicated relationships with radiation in general, that's why even the health impact of non-ionizing radiation needs to be investigated (yeah, your cellphone is most likely safe ;) ...but you know that you have at least some cells in you body that respond even to non-ionizing EM radiation - they are in your eyes and thanks to them you can read this :) )
http://en.wikipedia.org/wiki/Anatoli_Bugorski Note: You may want to avoid doing an image search though.
More generally in the short term it's fast growing tissue that's most at risk. So, exposure that is quickly lethal may not do a lot of damage to slow growing tissues. Long term you can often remove severely affected tissues so a person can often survive much higher doses to their arms and legs vs torso.
PS: Another issue relates to population sizes. A 0.1% risk to everyone in the US kills more than 300 thousand people and is a major issue. A 0.1% risk to one person may not seem that bad as that's around the default risk every month for a 55 year old male.