If she had "come out" to the crew as a Cardassian operative, but maintained good guy status ("We're all stuck out here together, Captain. It makes more sense for me to cooperate, remain a member of Voyager's crew. Admit it, Captain, Voyager needs the skills I learned in the Obsidian Order.")
That might have worked. Who knows, she might have even considered it. But she probably figured that if she had openly revealed herself as a Cardassian, it would have made her a target for assassination by the Maquis on the ship. She couldn't afford to take that risk.