I never understood what she was doing with the Kazon anyway. A single operative (especially a female in a male dominated culture) wouldn't have been able to build a power base in the DQ, neither did the Kazon have technological means to get her back to the AQ (plus they were little more than petty thugs who fought among themselves).
She never meant to stay with the Kazon. Seska is a user, and she was using them as a stepping stone to bigger things. I think she was really deluded enough to think she could capture Voyager.