Wouldn't encouraging cession mean MTG is now encouraging active rebellion against the United States? And wouldn't that make her ineligible to hold office under the 14th amendment?
You would think, but this is the second time she's suggested secession (admittedly she wasn't as blatant the first time) and nothing was done. I doubt anything will be done this time either. It wasn't even a major headline.
People are talking more and more about whether the 14th amendment bars Trump from running for president. If that ends up happening I think it'll end up being applied to other insurrectionist politicians.
Voicing an opinion, especially a political one, is pretty heavily protected. I think there would need to be some other crime being committed (e.g. actually taking up arms).