Use fire mark to hit her while she is healing. You can also find several walkthroughs of that boss (winged glory) on Youtube.

The ones on youtube look rather different than mine, I'm not sure if that's outdated or my old steam account is.
The boss I see on youtube videos has no shields and it gets hurt by Ekto Lumeh or Atul Aghni while flying around, mine can't, It only allows me to hurt it every second rotation.

Atul Aghni + Udah Notem while it tries to heal works but I am so done with the game right now.
It doesn't respond to spells properly, and yes I have done my custom voice recognition.
Maha'ki or English it has its own problems. Saying one spell but activates another is very annoying, especially after you marked the ground and you say Munio Namet, it mistaken it as Udah Notem. Also happens in english, "Shield Protect me" apparently sounds like "Unleash the flames", also at times when you say a spell and nothing happens so you miss an opportunity.

Great game though.