Anyone ever run into this situation ?

Every time I attack this fallen enchantress with my unit (Varda) she gets the damage done (-21) and then immediately heals over 3x that damage (+64)... thereby always staying at full health.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1555896735
How to deal with that ? And she doesn't even appear to have any special abilities it seems...
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1555897066

Is this a bug or it this part of the insane level experience ?