There Fixed it for you.
You seem to cling to this notion that Midular was honestly attempting to broker a lasting peace with the Empire, and not just trying to buy time to build up a force capable of fighting the Empire, Otherwise known as the Elder fleet. Ill give you that she would have taken a legitimate peace if there was one to be had. But lets think about it:
The Vindication wars were draining Republic assets, manpower, and resources, So Midular, as Ray of Matar, the leader of our people, makes peacefull overtures to keep the Empire off our backs and to free up those resources I mentioned earlier.
The Elder fleet meanwhile is being constructed in secret, because if the Empire had seen a massive build up of Republic Fleet, then that would have jeopardized the diplomatic overtures being made to buy time and would have invited either a preliminary strike or a similar build up of their own military capability - we would likely lose an arm’s race.
Muritor in the mean time, defects, takes a portion of the fleet with him and starts causing trouble as a rogue actor. This of course is a part of the Midualr-Shakor Plan to create precedent of rogue elements within the Republic, providing probable deniability for when the Elder fleet is revealed. He willfully gives his life over to Filmir, both to cement the narrative and to position Filmir as a capable, loyal, and key supporter of the Republic. Shakor is used as a foil, giving the more ‘nationalist’ elements of the republic some one to rally around, and more importantly, control.
Sisters of Eve find the existance of the Starkmanir Tribe within the Empire. This unfortunately is not part of the plan. The Midular-Shakor plan kicks in and the Elder Fleet is deployed before Schedule.
Simultaneously, Republic officials that have been compromised by the Amarr are executed, under Midulars orders, because who better would know and have access to the levels of corruption infecting her government? The Elder fleet and the purge are given the guise of being part of a fictional “elder network” a ‘rogue’ element within the republic. It’s already been established that the Parlimentary Republic doesn’t have full control of the nation thanks to the defiants.
Upon the return of the Starkmanir and the millions of freed slaves, Midular dissolves the parliament and calls for elections, handing power to Shakor with the intent of ushering in a Tribal council governing structure as the Sebiestor Chief, a position with more executive power than the Sanmatar. Filmir Emerges as a central figure in the Republic military in both anti piracy and the fight against the Amarr Empire.
Karin Midular was the Ray of Matar. She always worked for the best interests of our people, and she should be given the credit and recognition she deserves as a master politician and standard bearer of the Matari. May she find peace among the spirits.
TL:DR: Karin Midualr was behind the Elder fleet, the coup, and the Tribal Council.