The problem with eliminating Tuvok is that BOTH the Maqus AND StarFleet will be asking questions about his death.
I can see a situation where Seska's asked for extraction, Tuvok is in the way, and eliminating him would buy some time. By the time the Maquis have worked out she's the killer, she's been extracted and SF is one step behind so, by the time they show, she's back in the Cardassian field of influence.
Other than that, I don't see Seska simply killing Tuvok because he's SF. She might be untrustworthy but we've seen the Cardassians as being pragmatic. There would have to be some advantage to his death. Killing someone within your cell might give you some initial brownie points - but it'll make other people edgy round you too - and it's not exactly something you can repeat.
I would have liked to have seen a Seska who is stuck in a situation where, to get home, she has to go along with pretending to be Bajoran. Outed as Cardassian at some point, she still wants to get home but she's completely untrusted. A shortage of resources (and perhaps she has specialist skills) means she can't just be locked in the brig for 78 years. Paris would be in the same situation of being trusted by no-one. That would have been more interesting than the jumping ship to join the Kazon which makes little sense.