She was played by Abby Pivaronas.
Tiffany is one of the villainous bank tellers at West Bay Trust Bank, along with Leon, Madge, Jasmine, and Gloria. In fact, as Monk stated to Natalie, Tiffany was the most recently hired of the group. The five of them, along with bank president Peter Crawley, colluded together to rob their own bank. As Monk later stated in his summation, each person had a role to play. In the case of Tiffany, she shut off the bank alarm, making sure their crime wouldn't attract too much attention. The group drew straws to decide who would be shot to make their act look good, and Jasmine drew the short straw and was shot by the evil Madge, who portrayed the Russian robber.
At the end of the episode, Tiffany was arrested along with the rest of the group (except for Crawley, who was subsequently murdered) for her role in the robbery.