Depend on how you seen her.
She is and if not being turned in the future will be a thrall - or die.
Character wise she comes from the childhood and best friend, who was a rather blank character to somehow a partner, who thinks individually and shows her tooth to Sharon quite often. Obvious she also have a crush on the MC and is one off the 5 LI in the game (although I don't think that is confirm by Likeblones, but if she is not, then I give up
)
Will this change that she is a thrall and as such will/must follow the orders from her master? No, but she has evolve.
- Astrid is a dangerous loose cannon. If Calisto will find her, things will become for sure very interesting. Possible Astrid and Callisto knew each other or even Astrid was or is some sort of agent for her. Regardless I think she will let Astrid out of her cage and the Astrid will try to manipulate Callisto. What happens then I don't know, but the best end for Astrid would be that she is alive at the end. Perhaps thralled? Perhaps other (non-lethal) humiliated things?