I am thinking that the producers are playing some mental games. When you have already revealed 3 good singers and 2 bad, you are probably thinking that the last would be bad too. They are hoping the player will chicken out and take the relatively lower $20k payout. It almost worked too. She gambled and won her $100k.
So far we have had 3v3, 2v4, and 4v2. I wonder if the show will ever try 5 good or bad singers or if will just be those three combinations.