Mörderin by Natalie J. Case

Seeking to reunite her family, Thána and her mother Alaina head back to the world where Daria lives with her husband and son.

The once vibrant city where people traveled freely through a collection of portals has been reduced to rubble, and Daria is now a prisoner of the invading army. With her magic still in nascent stages, Thána agrees to a daring and dangerous rescue mission with Daria’s husband and friends, once again putting her life on the line for a family she barely knows.

To make it work she has to push her magical skills to their very limit and rely on those she’s only just met, not to mention breaking into a prison camp and getting out again in one piece. How hard could it be?