You are almost there. One province of Kaiserin Konstanze is remaining in the east. That should be Felssenke, her home province, where she and the witch are hiding.
- Scout eastern province
Indeed the province to the east is Felssenke. And there you will find the castle of Kaiserin Konstanze, too, where she and the witch are hiding.
Previous Quest: Reach To The East
Next Quest: Yet Another Curse