This is just a matter of opinion, but I think Selena must have been the one to use the tome. I think because of the way it works, Selena would have to tell them explicitly how to use it if it wasn't her.

In that situation Selena may have been using it to either attack or defend. And if no one has wounds on them...then it could only really point to two people then.

[The ones with protection that is to say.]