Wendy x Bronya
, when?
That ship got sunk with extreme prejudice by Mommy Dearest to power a GIANT ROBOT rather quickly, I'm afraid... (´;ω;`)
What an ungrateful little shit...
It's called being in shock. Most people don't deal with sudden displays of violence very well without a certain amount of mental conditioning to prepare them for it; Seele would already have been under serious emotional stress here and watching her BFF coolly slaughter two people like so much cattle to top it off clearly rattled her pretty bad. (She's presumably well enough aware of what Bronya used to do for a living but witnessing it firsthand is a whole different kettle of fish from vaguely knowing it as an intellectual abstraction.)
Plus going by how she reacted to witnessing what Sin did to Bronya she probably has any number of violence-related prior traumas anyway. One rather gets the impression the kids Kokoria/Kukuria/Kakaria/Cacalia/Cocolia (seriously there's like 0 consensus or consistency to how her name gets translated) takes in generally haven't had particularly happy and wholesome childhoods...
On another note, I wonder if that grim reaper vision isn't partly referencing Seele's stigmata appearance...?