I don't think Acacia is a valkyrie. The tattoos on her hand are probably significant to what she is. She might've just come across Tamsin one day and trained her in the ways of being a bad ass. "Why do you care so much!?"
Are they filming 4x11 or have they already moved onto 4x12?
Well, the read through was for 4x12 right? I am not sure whether they do read-throughs while shooting the previous episode or if they do them right before shooting that next episode. I'm gonna go with 4x12 judging by Anna's tweet of "shit getting real".