Here is the things I take as canon for the sake of playing Beatrice:

Canon:

- All eight chapters of the visual novel + the Magic Ending.
- Confession of the Golden Witch (manga-only special explaining Yasu's past.)
- Answer of the Golden Witch (Interview with Ryukishi07 laying out the truth of Umineko)
- General Skhannontrice theory. (Though Yasu was plotting to kill the Ushiromiya family, she was not the culprit.)

Questionable Canon
- Our Confession
- Golden Phantasia (Only in that the XXX forgery exists.)
- The Tips Collection

Not Canon

-Anything related to Rosatrice.
-The whole Ikuko = Yasu thing.