I checked myself - yep, it's the same:rolleyes:
It's just a bug in the special ability.

Any suggestions for other heroes?

Maybe she should just not give her demons, and come up with something else? Like, the attack of creatures increases if they fight against "evil" races.

Dark genius.
All spells from the Darkness school cost 1 mana less for every 10 levels of the hero. In addition, the hero learns the Grief spell (common).

Hunter.
The hero can set traps on the map. If an enemy hero falls into it, he may lose an artifact/part of his army. The probability is 10% + 2% per hero level.