You're not "wrong," but I can still save this disloyal Commander theory that saves the seriousness of the episode.That idea doesn't comport with her behavior once captured.
• She's been immersed in double-dealing and intrigue for so long that she's still playing her loyal Romulan role aboard the Enterprise from deeply-ingrained (life-saving) habit.
• Also, the Enterprise is intermittently communicating with her flagship, and if the flagship picks up the tiniest hint that she was spying for the Federation, Tal could be investigated and executed. He was her right hand man in the scheme.
• Third: if she's a smart, disciplined spy, she has a task plan detailing when she'll do what. Her plan doesn't say "Laugh and slap Spock on the back the moment you're off your flagship." Kirk and Spock might not learn she was their helper until she has officially defected, and she'll drag that out as long as possible to let the trail go cold on any Romulans who share her ideology, and possibly even to keep the heat off her family. If Romulus is anything like North Korea, her folks could be sent to a concentration camp for what she's done. She might ask to quietly disappear into a Federation colony and never "make the news" at all.
