No critiques after almost two months? I'm ashamed of myself.
Anyway, I enjoyed this Black rose chapter, but I also feel a little lost. This could be the writing group problem, with my reading of these chapters spread out over months of time, but I feel like I missed something. I don't get a sense of Black Rose's motives at all—she's helping the invaders, but why? I don't see Sericea in her anymore. Kind, loving, self-sacrificing Sericea became ice-cold, heartless Black Rose the moment her imprisonment was broken. Is the woman who cared for Rosalin so tenderly really the same woman who gazed dispassionately at the carnage left by a raging Shifter?
Maybe if we knew more about the person she was before she was imprisoned. We know she gained a forbidden dark power, but we don't know what drove her to it. What was she trying to accomplish then? What is she doing now? It's not quite clear.
Maybe if we knew why she was who she was in that town. How does she have a sister, when she's over 400 years old and apparently hasn't aged a year in all that time? How did she keep people (and most especially, her sister) from noticing this fact?
The one viewpoint per chapter system is working well for you. We got a good solid chunk of story instead of a lot of bite-sized ones, and it's more satisfying. Your descriptions, dialogue, action scenes and the flow of the chapter are all well-written. My main gripe here is the character who at this juncture doesn't make much sense.