Even though her blind fervor, part of the flagellant did realize that Olivia's foolhardy charge had kept the other demon away from her whilst she was still dealing with the first. She had no outward reaction, but a mental note was made. A blood debt.

Rage carried her arms forward through the pain, and hate guided the blade down upon the creature's exposed back.

SPOILER! :
Oriel continued the Greater Frenzy!

Full attack;
1d20+20=27, 1d20+15=33, 1d20+10=21

Damage dealt;
2d6+7=12, 2d6+7=15, 2d6+7=12

The second demon is now down to 19 out of 70 HP.

Oriel's dress was now red. The thing wasn't quite dead yet, but... judging from the macabre look on Oriel's face, that may not have been entirely unintentional.