I voted for the cobra, but I'll just note that it won't be possible to keep the stats completely the same – you wouldn't want to leave her with flight.
Well, the point of flight is that walls are no obstacle for her, and what I saw in the animation of her movement underground, i.e., below the walls, is very similar... but the ability name will have to be changed... for consistency!

---------------------------------------------
Неудачное планирование ведёт к неудаче ...
NCF - мод, добавляющий дополнительных существ в HeroesV 3.1