Helga endured the pain. She was casting a spell when the backstab hit. The stab didn't cause her to stop casting.
Kaghast also ignored the fire damage from the flame shield. He activated Warrior's adrenaline rush, increasing his attack speed as he delivered a flurry of stabs to Helga's body.
Helga's spell was completed. An intense hurricane of flames erupted with her at the center. This flaming tornado engulfed Kaghast who refused to retreat.
Kaghast's body was covered by a translucent light, reducing the damage he received from the flames. The protective light was Ki Armor. He also used Ki Weapon on his katars. Aside from that, his body hardened and became stony. This was Battle Monk's non-standard skill, Stone Body. Aside from increasing defenses, it also negated knockback and increased the user's body weight by many times. This increased weight made him resist powerful force which should have blown him away.