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Uff... Finally managed to deal with this lady :)
It didn't work out in 20 minutes, as they said here; it took me three evenings :)
In general, when I came to her for the first time, her army was already significantly superior to the armies of Railag and Shadia, and I only had 3 unbuilt Necropolises and 1 Castle in reserve. In general, I had to return and capture all the castles, and everything else along the way.
To, as they said here again, accumulate more human troops.
But in the end, no matter how much I accumulated, Isabel always had twice as many. Apparently, she had the Tear of Ashi, and she was constantly training troops (I just can't figure out where she got the finances from).
In short, after several unsuccessful attempts and another gathering of troops, I attacked again, this time she had about 1K paladins and a couple of hundred archangels + some other units :)
Realizing that it wouldn't end today, I gave up and set it to autobattle...
And that's when the computer came up with a simple, almost stupid solution, namely - constantly create phantom archangels :)
Realizing that not all was lost, I rushed into battle.
Although they were firing from the towers relentlessly, the phantoms managed to do their job.
The coolest thing is that each new phantom can resurrect fallen soldiers, and the phantoms of the 120 archangels that I had, each time raised about 10,000 hit points :)
And you say that the computer can't come up with anything good :))
Forgot to mention, I was, of course, taking down this villain under the leadership of the great mage Zehir, for which he received about 300,000 experience and 2 levels :