Sayo is distinct from X Beatrice, they are two different people.

Leads:

• The Leg Tattoos are too conspicuous of a detail to not be intentional, and they leave no room for doubt.
• Beatrice is not "one individual woman" according to Bernkastel.
• The two of them interact in the meta layer near the end of Alliance in a way that suggests two people with similar goals.

Leads:

• The face is the same.

Obstacles:

• optional

It was X beato, not Sayo, who had a coping mechanism that Battler destroyed.

Leads:

• The sin is not between him and Beatrice, who we associate with Sayo.
• She is the one talking to Battler in reality during that scene. She has the outfit and at that point Sayo is probably dead, (although we're not 100% on that).
• In the meta layer she is the one with regrets about the sin, and she looks hurt after he doesn't remember.
• Crunter said so and that's the best answer we got.

The supposed corpse of Shannon isn't hers and it also isn't a corpse. That is simply X Beatrice trying to hide herself with the help of the adults.

Leads:

• We can beat the red by simply claiming that the person there wasn't dead and thus not an unidentified corpse.
• Maybe after seeing the girl from the portrait show up the Ushiromiya parents want to keep it a secret in fear for the inheritance.
• There's room for a 17th person in Legend.

Obstacles:

• Does the motive make any sense with the whole murder going on? Would this be the priority of a bunch of greedy but otherwise innocent people? And are the kids really the ones to whom this secret needs to be kept?
• Her presence isn't required for any Legend solution, and her being here would break an interesting pattern with the episodes.