Why is she assuming the manga reflects actual events? I mean, even if she wholeheartedly believed that Yurina is a magical girl, if you find a manga about you featuring events you don't recall, the natural assumption is that it's fictional.
Honestly, the obvious answer in any remotely sane world would be that Yurina is actually an artist and a magical girl fan who is writing a manga based on her fantasies. Even if that's supposed to be blood on her arm, that would be the first indication she's had that any of the manga events actually happened.
That would actually be a pretty cool way of how the story would progress. Just to add Yurina probably has more of an obsession towards the MC then the cheerful girl that she is presented, maybe also a chuunibyou to boot since she makes those manga.
The series going forward can explore her mental state and also the dangerous ways that she tries to recreate the scenes that she is drawing about. Also her crush on the MC may be able to lead to some Yandere shenanigans if that the above is true ^. Would be an unexpected great read if that is the case.
Hopefully more updates would come soon, although I have my suspicions that this would only be 2 chapters and that is all since this hasn't been labelled as a series itself. That would be sad...