Hi,
I think what your daughter has here is a successful science experiment. Iodine does not naturally occur in most salts. It is something that is added to "iodized" salt to promote better health. See this site for more information:
http://www.saltinstitute.org/Issues-in- ... se-in-salt
The results your daughter got are probably accurate. One thing she can do is study the FDA labels that should be on the packages of purchased salt to see if the manufacturer has iodized their products. If she sees that one product is iodized, but her experiment did not detect any iodine, then the experiment is not ruined. Your daughter just needs to sit and think about why she got her results, from what she knows about the basic research she did as part of her project. Getting negative results in scientific experiments is part of the process. When we get negative results, we are forced to ask ourselves why and then go correct the error we made, which might be an experimental error or maybe it's an error in our hypothesis.
These science projects are always educational experiences for us all.