NHF – new heroes for Heroes V 3.1.

On one hand, yes. But on the other hand, the balance needs to be calculated specifically for those who know how to play (another option is technically impossible).

There is such an option; you can replace her starting spell or give her Stone Skin as an additional ability (logically: gems are stones, stones are earth, earth is spikes).
But this is just one of the options.
By the way, I just remembered. Ula is a shaman from Heroes 6 (the very first mission, where she was kidnapped by Togrul). Is this the same one, or is it just a coincidence? (I haven't read the description, but I watched the mod on Remixa's channel).