They hadn't ruled out the wrong answers.
When the Sword Maiden announced the answer was incorrect, Ash felt everyone breathe a sigh of relief.
Unlike the first question, which was full of age characteristics like the middle-aged peasant woman and the little girl, the three people in the second question were all about the same age, and none bore any resemblance to Sonia, clearly not sharing a familial relationship. Moreover, the question was about "the person she hated the most," so it was highly likely that none of these three people were even friends with Sonia, making it impossible to analyze any further information. Therefore, Sonia could only choose the only person she recognized—pure white Diya.
But if the answer really was Diya, then things would become complicated: why did Sonia come to the amnesiac cabin with the person she loathed the most? Could she have been framed? Should she take this opportunity to deal with the person she hated most?