Tiffany has her eye on the money as well, and as much as I prefer Claire to Alyssa, she should have heeded Alyssa and put up Claire. That would have ensured that Claire got to play in the Veto competition and Tiffany could always have changed her mind and backdoored someone else.
But Tiffany should have known that when they agreed as a group who would win the competition, and she went directly against it with no explanation, it'd make them irritated at her. That's just failure to maintain positive relationships with the other players.
I don't think she's being unreasonable, I think she made a terrible game move.