...Having "Resurrection" in her arsenal, she was invincible. Her army didn't even dwindle.

I only got "Resurrection" in this mission, at level 5 of the Guild of Mages, in the second captured Castle, the human one, located near the exit from the dungeon, formerly turquoise. Before that, I had to make do with "Subjugation" and "Battle Frenzy," as well as "Raise Dead," and Frieda acquired "Create Phantom" in the "Duncan" mission, when capturing his Castle. Thanks to "Subjugation," I managed to conquer that very first human Castle:smile02:! By the way, at the same level 5, I also got "Portal to Town," which is also great:smile03:.
To attack the garrison guarding Duncan, I would go to the "improvement tower" and turn Angels into Archangels.
By the way, about companions, I hired a former turquoise player, level 24, who was sitting in the first human Castle about 3 days after I captured that very Castle. This nasty fellow, like my Frieda, has a Guardian Angel - when I captured his Castle, he resurrected as many as 196 militia... But Frieda and I still defeated him:smile13:!
What is the maximum level Frieda and Duncan can reach? For now, she is level 27, and Duncan is level 23. I keep fighting, but I don't see any progress. In the witch's hut, I only got "Battle Frenzy," but we would like "Phoenix":smile08:...