The key word in eliminating B is "might." The given principle tells us that Shayna can misrepresent her feelings if she believes Daniel would prefer kindness to honesty. However, B gives us no indication that she believes this. It only says that Daniel might prefer kindness to honesty.
We do not know what Shayna believes, so she does not qualify for the exception provided in the principle. Therefore, she should not congratulate Daniel. This is why E is correct. If Shayna has no opinion, then she does not believe that Daniel would prefer kindness to honesty. Because of this, the principle dictates that she must choose honesty.