In the book the westing why did the judge think sandy was really sam westing?

1) Dr. Denton Deere told Judge that her partner, Sandy, "sure could have used some [plastic surgery]...", because Sandy had a "battered face: the scars; the bashed-in-nose..."

2) Sandy's behavior during the final meeting in the Westing mansion (towards end of book) was suspicious to Judge, as she ponders why Sandy was purposefully "leading the heirs to Crow."

3) She finally pieces everything together realizing that Sandy was "the one person who could confound her plans, manipulate her moves, keep her from the truth. Her partner, Sandy McSouthers, was the only heir she had not investigated."