Hi Philip! Your answer is really almost right, it would be "A ella le preocupa la radiación"
The explanation is simple: the verb "preopupar" works as "gustar" in Spanish, I mean, it´s the radiation that makes her to be concerned, so "a ella" operate as an indirect complement.
It´s clear more or less? If you haven't understood I could try it again, just say it to me :)