After Alessia ran away, the frog monster first started to chase after her but failed to get out of this area of the dungeon. It had appeared in this room because Alessia's team had mistakenly triggered a trap that they had failed to notice at all. But now it was the monster who was trapped in this area.
It was also quite hurt, so now that it was free, it started healing. Nina, who came to scout the monster after recovering a little bit noticed this and informed Alessia immediately. Hearing that the monster was trying to rest and recover, she decided to not give it the chance. She was not sure how much the monster was capable of healing but if it could regrow the fallen heads then that would be game over for Alessia.