Thanks for asking for such a "what would be" detail, it's fun to think about and I love that Red Queen is so well thought out such questions are invited to be asked and be answered.

It's so "would be" because Tiberias and Elara are both dead when Monfort makes its great reveal, so there're two angles to this question: What would be if they had lived when the reveal is made? (Or did Monfort wait for their deaths?) And what if they secretly did know about Monfort before they died in canon?

About the latter angle, I imagine the passive Tiberias wanted to do nothing about Monfort as long as they don't bother Norta. Elara did not like that and wanted to at least get more intelligence. In this regard, it's also interesting to ask how much influence Elara had. She obviously wanted more power but Tiberias didn't give it. After all, if she only wanted a crown for Maven, she could've focused on killing Cal instead of going for this risky two birds with one stone coup of making Cal kill his father that nobody believed anyway. What did Tiberias do that Elara wanted him dead?

Possibly, Elara felt threatened by Monfort. I remember one country got rid of all whisperers and I think she was afraid of that. I believe that were the Lakelands and not Monfort though Elara feeling threatened of other countries following suit could be a real thing.

In the long run, Elara must've seen the danger of reds knowing about equality and democracy working and wanted to put a stop to it early on. That's the intel phase that, in Norta, would also have her set up a misinformation plot where the only news about Monfort would be misleading, negative and making Monfort seem weak and unimportant.

This scheme would grow bigger if Elara had lived during the reveal of Monfort itself. It would no longer be some random news among the relevant stuff but a large campaign drawing a horrorshow of Monfort, derailing democracy as weak and dangerous. You can see this happening where autocracies in real life agitate against liberal democracies, aiming both at their own populations and to doubters in the west to turn them into conspiracy ideologists as Russia Today did. Elara's aim would be mainly the reds, to scare them away from looking for inspiration from Monfort by promising violence and chaos, but there might also be silvers who just don't like the Calore monarchy. Feudalism and monarchy doesn't give anyone not in the high houses or just nor favoured enough by the Calores a voice and power, either, while Monfort also offers silvers voices in parliament and making it work. Knowing such a society exists prepares the soil for dissent that can't be tolerated by the crown. A part of the misinformation would be "news" about violence against silvers.

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Montfort Fortress