It was Cane's fault for not making things clear for her. Yes, they could have safe sex now that Cane could control himself better and Iris could keep up with him, but they had never really talked about having a baby.
Cane just assumed that Iris already knew the purpose of the concoction from Grace, but right now, he started to question it.
However, on the other hand, it was not Iris not realizing the ultimate goal for all the tonics she and Cane had been drinking regularly, but it simply didn't cross her mind last night when she drank the alcohol.
She didn't think about it at all. The only thing in her mind was; how to bond with the five warriors and knew more about the Howling Wolf pack. Deep down, she still had not yet completely given up.