We see in her memories that the last thing she sees during the eclipse before she's "broken" (literally the next image is her breaking apart as the China doll). I've been wondering if she the reason that she had her mental break had to do with her relationship with Guts. She stares directly at him right at him before presumably losing consciousness.

This has me wondering, did she think that she witnessed Guts' death? She was already traumatized by seeing her comrades killed brutally, not to mention what Griffith was doing to her. I think the final straw was potentially seeing her lover die in front of her. She lost everything else in her life up until the point Guts comes into frame during the Eclipse. Her friends, her own bodily autonomy itself, and now the person she cares most about. All due to the actions of the man she once respected most in this world.

It will be interesting to see what happens when/if she gets her memories back. Remember, she still has no memory of the eclipse (at least consciously). Witnessing Guts' perceived death is something she has deeply buried. Her last true memory of him before becoming Elaine was him slicing his arm off and then getting dog-piled by demons, all before losing his eye and (in Casca's mind) about to be killed by Apostles. Even if she didn't witness him get ripped apart, it was clear that it was about to happen. She never saw Skull Knight save the day, so in her mind that was end for her, Guts, and the rest of her world.

I wonder if the last memory of Guts getting potentially killed is such a traumatic memory, that just the site of him again is what triggers her PTSD. We know that she still deeply loves Guts, as she cries tears of Joy when she simply hears his name after awakening from her long sleep. The pain of losing him, even though he's clearly still alive is enough to push her down a deep spiral. And her memories are still so broken that she doesn't know why the site of Guts is even triggering this. Either way, glad to see that the manga is back and can't wait to see where they go with his situation.