....
As Felona tried to protect her people, she kept exhausting her spirit essence, which had already been weakened by Eren's poison. This poison had forced her to waste a significant amount of her spirit essence.
If she had been solely focused on fighting, disregarding her surroundings, she may have been able to fight back effectively. However, in this situation, she found herself on the backfoot.
Her body was surrounded by a protective aura of spirit essence. She managed to absorb a great deal of the fire's destructive energy, containing the flames within a small sphere that was shielded by her spirit essence.
She realized how unstable it was. It was only a matter of time before the flame was going to break free if she didn't do anything.
After condensing the sphere to its limit, she absorbed it into her body, even though it was no different than poison for her.
