I finished it even before the comments on my post appeared. But thank you anyway! I won't be able to check Frida's stats, but she was level 25 or 26. I couldn't level her up more than one level during the campaign.
Added 26 minutes later
VIPmd
I did it in a clever way – I paused the heroes (you can do this if your computer is powerful enough), transferred 900 Cyclops to the woman, and then nothing could scare me.
But I also played it fairly! Kujin was defeated, but with heavy losses. Then, contrary to my expectations, the message about the lost mission didn't appear. His companion remained standing near the castle; I attacked the demons with him, killed them, and returned to Zehir. Zehir walked around, I clicked on the end of the turn, and saw that the Orc ran towards the exit, went outside, and, as far as I could tell, headed towards Zehir. But I was too lazy to watch where he was going; I had already struggled enough with this campaign. So, I continued playing from the save after Kujin's victory.