My guess is that the "friend" is her real sibling, probably her bro died some time ago (maybe this boy killed him -haha jk, that'd be too dramatic-) so he's willing to take care of her as some kind of promise to him? Maybe that's why the wing of the butterfly is broken, or maybe they had a fight and he feels guilty towards him and that's why the glass of the butterfly is broken. Anyway, I'm over-reading the last part but I feel that's the connection.
Tnks for sharing <3
Ps. Oh gosh, she's willing to ignore how weird is this whole mansion just because she doesn't want to be alone once again