I think she knew that either Bob or Matty would hands down beat her, so she would lose regardless. I felt like putting Bob in a tie break with Matty was her way of "letting the best man (fire builder) win!" And, it was up to them. I think she really likes both of them and would have been happy for Matty if he'd won.
The fact that Susie got any votes was a huge surprise to all - especially Jeff Probst - could he be more obnoxiously obvious about his disdain for Susie!! But, the vindictiveness ran deep - both against Bob by Kenny and Crystal, and against Sugar by the onion crowd.
*** totally cross posted with AST