Agent T is a secret agent turtle working for the O.W.C.A. in the Easter Island.
While strolling, she spotted Candace in the Easter Island trying to get her phone from a bird. She informed Carl, who then contacted Agent P who used Heinz Doofenshmirtz's "Pick 'Em Up-inator" to bring Candace back to Danville ("Candace Disconnected").
Unlike other agents she has a black fedora. This could mean some kind of age as since in the 80-90's the usual fedora color was black. However, her fedora is brown in another shot, which could simply mean a color error.
Because of no gender being stated in her first appearance, a few (or most) viewers thought of her as a "he".