a couple weeks have passed since introducing herja and it seems the OP was right by her adding 30 morale, she never crits, doesnt do damage and seems to always debuff -5 morale if it lands.
which can also be frustrating. for several reasons actually, like the most obvious is that iron set with spirit retains 65 morale and if she adds 30 each round then you are just 5 morale short from a complete new horizon in tactics opening up. but also like suggested above she should be able to improve, to get better. it doesnt really matter how, if with stars, gear, weapon or even by level. if not being able to improve the amount of morale gained it should be at least improve the amount of morale on the debuffing. point is, -5 morale can really screw up someone if they havent encountered it before, but the easy fix is to increase your morale runes to +110. so investing into herja to make her more effective and i am thinking about deducting a percentage instead of a fixed amount. a percentage that you are able to improve by for example adding stars on her, increasing her magic attack, etc... from the game play view it would make more sense too since it seems silly that a herja with an apprentice staff can do the same as someone else with a justice staff and all slots filled. so why even give her magic attack and not just set physical and magic attack to 0 to avoid confusion.
now from a developers point of view it should be in their best interest to be able to improve herjas casting because it would also increase the "in game economy" by forcing other players to get better weapons, gear, to buy cards to sanctify her and to buy stars to make her really rock.

i would like to see her improve a certain amount/percentage of her morale buffing/debuffing by improving magic attack, amount of medals and level.
it could be something like:
- the magic attack increases the amount of morale debuffed
- the level (experience) increases the amount of morale gained
- stars/medals increase the amount of on gain and drain

now this should make a lot more sense to other players, it should improve the game play, the economy and should make players and game makers happy, wouldnt you agree?