There were only a few ways the Central Church could attack—and at this point, Edelgard would be honestly surprised if they didn't. They couldn't hide anywhere, at least; not if they still wanted to claim themselves knights and priests serving the goddess. She would know by now if they were anywhere accessible.
Still, even with the limited options there was a lot to consider. Since the Knights of Seiros hadn't been seen in large numbers since Cornelia took Fhirdiad, it could be assumed that Rhea retained their full force—or something close to it. Edelgard had no doubt that she could still outnumber them, but she didn't want to underestimate them purely based on that.
Edelgard's main concern was for how the knights would come. When she took Garreg Mach at the start of the war, they fled through some passage—she was able to have a group follow them and block off the path, but they had left long before then. Even if anyone she sent out couldn't find any more passages, Edelgard expected there to be at least one.
She couldn't entirely tell if she was fully prepared or somewhat paranoid. Oddly enough, she had more chances to talk with the others—former classmates, Byleth, Claude on a few occasions—than she would have otherwise. Maybe it helped that work was light, and the next best productive thing to do was train; a lot of them seemed to have the same idea.
It was almost a relief to hear Knights of Seiros were seen in the area near Garreg Mach on the last week of the Lone Moon. Fitting—it matched fairly well with her siege of the monastery. Both sides could twist the date to their advantage; one to right a perceived wrong, and the other to end the war as it had begun.
Edelgard gathered a majority of them to give the order.
"The Knights of Seiros are appearing west of Garreg Mach," she announced. "A few small groups will be going out the meet them, while the rest of you will be divided between here and the town outside the monastery. There are a handful of knights—and some former students students, if Rhea's making them fight as well—that should be captured rather than killed. I expect a majority of them to be commanding the others. IfRhea is fighting with them, focus on her—if not, focus on the Knights of Seiros as a whole. This will start the final battle, whether the end comes today or after another search and pursuit—there's no need to fall without reason."
The soldiers agreed, and she carried on to specify who will go to face the knights outside of the monastery; when they left, Edelgard sectioned the rest of the army so they were all in groups, with at least one person who could recognize the knights or students in each. Partially through silent volunteering and her request, her own group was a familiar one—the same people she's been fighting alongside since the start, as well as a few others to add some numbers.
There wasn't much for her to do immediately; she waited in the entrance hall to give further orders if she needed to. It didn't take very long for a report came saying that knights had entered Garreg Mach—since the walls hadn't been breached, Edelgard gave instructions to those closest and joined them in fighting.
Edelgard focused on the knights that had entered—they came in groups of about two dozen, and from multiple areas. The mix of Imperial and Alliance soldiers in each area outnumbered them by at least ten people, if not more, as long as none of them wandered too far or abandoned their post altogether. She wondered how many of the knights noticed that.
She stayed near the main gates of the monastery when they were all dealt with. There was a brief lull in fighting the knights when someone came up to her; she could recognize him as the leader-of-sorts of Abyss. Oddly, the actual underground area seemed to be devoid of any used passageways outside of the monastery.
"Have the knights started coming into Abyss?" Edelgard asked.
"Not knights," he replied. "Mages. It seemed like something you would like to know, since they're not friendly."
"It is, thank you. Let the Kingdom prisoners take care of them, but don't let them leave Abyss. I'm willing to pay your people to fight based on effort, if someone reliable keeps an eye on them to tell me how much they deserve."
He nodded and left to tell the others from Abyss. Edelgard just had to trust that Dimitri and the former Blue Lions would all be able to fight the mages efficiently. There were still enough soldiers to comfortably split between those who slither in the dark and the Central Church, but only if the ratio between her soldiers and the knights stayed even and if the mages didn't have too many with them. She assumed they were there to add to the casualties; there were grander places to stage a full, dramatic battle to remind her of their power. To make her regret anything.
She wanted to stay focused on the church and, for the most part, the opposing sides seemed willing to let that happen—as long as the mages stayed in Abyss, the knights wouldn't notice them. Even if they did, there was a chance that Rhea would have them kill the mages as well, despite it ultimately aiding Edelgard as well.
The groups of soldiers sent to deal with the knights outside the monastery returned, providing reports of a cleared area. The later few, coming back roughly two hours after leaving, told her that a group of knights was heading towards Garreg Mach directly instead. With the previous groups of knights killed and the places they came through investigated and closed off, Edelgard gave another order to meet this new group in the town outside Garreg Mach.
About thirty knights came; leading them was Alois, who recognized Byleth standing next to Edelgard. He merely seemed to steel himself, then gave the order to the knights around him.
"There will be more coming soon! Let's clear a path for them!"
Edelgard wondered if it was mostly a calm façade, or if he genuinely believed the Empire and Alliance together had lost any great number of soldiers. Either way, it only took two allied groups to put his to rout, even if the knights fought valiantly; Edelgard approached Alois when he had enough wounds to be unable to fight.
"…I take it this is the part where you kill me?" Alois guessed, somewhat looking up at her but wincing.
Edelgard gestured Byleth over. "Actually, it's the part where you thank Jeralt and Byleth for considering you a good enough friend to spare. For now, you'll be somewhere else until the battle ends."
Edelgard took Alois's weapon, and Byleth offered her hand to help the knight stand. He accepted with partial hesitance.
"I just want to confirm something before you're taken somewhere away from the fighting," Edelgard said. Alois gave her his attention. "Is Rhea planning to attack soon?"
"…She is—but she was careful not to say when, even to the knights."
"That's good," Edelgard said, nodding. She looked at Byleth. "Take him wherever you think is best—I would like to have you close when Rhea comes, however, so please come back after you've confirmed someone can watch him."
"I will," Byleth promised.
She left, leading Alois away from behind. Edelgard made sure the soldiers around them knew that Rhea was among the enemy soldiers, then waited for the next group of knights.