While Lou was away to ask Aliana, Iris thought about the whole thing and tried to use her power on the poisonous food and water. Still, she couldn't feel the black magic, only this a faint vicious feeling.
The poison must be related to the black rain somehow, but she couldn't put her finger on it. It was still confusing for her about how this magical power worked, since Haco's health had been deteriorating rapidly and she didn't get enough knowledge about it.
Iris still had not yet learned about what actually happened to her old friend.
Therefore, having Lou by her side and for him to answer her question was way more helpful than having a conversation with the Serafim.
At this point, her respect for them had hit the rock bottom.