User blog comment:Angren Túrë/Ruby Backstory episode; "Cloaked in Roses, Part 2: Summer Rose"/@comment-107.15.104.101-20130731130534/@comment-4830106-20130731134354

I'm probably going to stray even farther afield by doing this, but I'll see what I can do to address your concern.

Everyone has their psychological pressure point, a fear that is just too powerful for them to cope with. For example, if you're familiar with 1984, Winston's breaking point was rats. Ruby's breaking point, however, is not something she is consciously aware of, even though it exists. Like most people, she wouldn't be able to easily say what her greatest fear is. As I see it, however, Ruby's greatest fear is being helpless/powerless, which could possibly explain her advanced training and fascination with weapons.

In the flashback scene depicting Summer's death, Ruby was already pretty nervous about the setting, and the fact that Summer's spirit was not there to guide her. Add to that the traditional subtle horror conventions like the torches and the laughter, and Ruby is already terrified, even if not in any actual danger. She also knows that Summer is about to die, and she has no idea how, but Summer's spirit warned her it would be pretty grim. And then the Oni mask that had been floating around in her recurring dream shows up, and Ruby's resistance starts to crumble.

Those are just all the factors that add to Ruby's current fear, and make watching Summer's death harder to handle. Whenever Summer attacked Graurim, he either ignored it completely or directed it back at her with little to no effort. And of course, when Graurim took the offensive, Summer was powerless. This struck a nerve with an already freaked out Ruby, and the added sensation that she was watching her own death in a past life certainly didn't help.