That's not Miyu, is it?
I think her frontal hair bangs are way shorter, even if she'd suddenly otherwise have long hair (covered by the cloak).

Not Miyu, the facial structure is wrong for Miyu. Don't remember her, must be past ep13

She's from the past in the last great war, she was the senpai of Miss Maria apparently and had to fight her friend in the war. I don't remember all the details, it was prior to episode 9, the episode where they got into the library.

It's Monica.