She is ... a mighty huntress.
After spending time on lap and table (the center of attention) during our class, she got let out, and was seen stalking through the courtyard. And she was successful, too. I saw the evidence quite clearly. Memories of Maya's younger days.
Even if she had gotten let in, I think I could have dealt with it. She ended up sharing with Julian (awwww).
Brigid and Julian were last seen squeezing their large bodies into a particular gap in the fence between the hall and the school. Must have been where the mice were hiding out from the rain.
I also think I know why there are no cat doors into the sanctuary so the little darling may go in and out as she pleases! That. Would. Be. Bad.