Chapter 692 - Retriting
Emma already retreated far away from the place. Currently the first poisonous Centri already created a layer of poisonous gas to protect himself. That layer of poisonous gas also works as a barrier to protect that Monster from any outside attack.
It is just compared to any normal attack, this layer of smoke did not have that much difference and this is the reason that all the time that Monster needed to move from his place to protect himself from those attacks from Emma. On the other hand the second monster was already shooting poisonous balls toward all those places where it was able to sense the vibration which got created because of the spiritual fluctuation.
Because of this, Emma is unable to stay in the same place even for a second. She just moved from one place to another place to escape from that place. She can't stay in one place for that long as the 2nd monster is attacking her direction continuously.