The actress explained in an official CW video that her character's true allegiance would become clear in future episodes.
"Season ten for Tess is going to be about whether she's good or evil," she said. "Over the past few seasons, she's been a little wishy-washy with that, and I think this season we're finally going to figure out if she's on the good side or the bad side."
Freeman claimed that despite her past crimes, Tess was "good at heart".
"Her morals are a little questionable and she's very power-hungry [but] I actually think Tess is good," she argued. "I know that might be difficult [to believe] because she likes to kick people to death and she likes to shoot a lot of things!"
She also suggested that the theme of the final season will be the final steps in Clark's journey towards becoming Superman.
"I think that's what everyone wants it to be [but the writers] don't really tell [the cast] that much," she said.
Smallville returns to The CW on September 24 at 8/7c.