Sana's unpredictable nature is exactly why the trio voted for her. She appreciates favors and she can support them any time. After Asim sacrificed his belt for her captaincy, she was genuinely touched and said that the house runs on the tit for tat basis. It might look a bit foolish, but it was better to save her from nominations than losing their votes.
She even appreciated how Rashmi honestly admitted that her first choice was Asim or Vishal.