Isola is happy to tell Juliet about Elizabeth slapping Adelaide. The U.S. wanted to minimize the stress and tears, so they had volunteers walk kids to the ships instead of parents. Isola had one group of kids, Elizabeth was playing games with another, and Adelaide had a group singing a hymn. Then, Adelaide told her charges to pray for their parents and to be good so that their parents, if they died, could look down on their children from Heaven and be proud of them. The children were distraught. Elizabeth told Adelaide to be quiet, slapped her, and threw her out.
By volunteering to care for the kids, Isola, Adelaide, and Elizabeth share the emotional burden of having to send the children away to an uncertain future. This is true even though Adelaide botches her attempt, though when Elizabeth is successful in throwing her out, it indicates that people can take control of who exactly is a part of their chosen family and cull as needed.
The shock of seeing Elizabeth slap Adelaide seemed to snap the kids out of their fear and sadness. Isola says that it was a sad day and she's glad she didn't have children. She tells Juliet that she's glad that Juliet had the Starks when she was a child, and says that Clovis Fossey wants to read her winning essay about chickens. Isola says she also hates chickens and that the Society would love for Juliet to visit.
Because Isola wasn't a mother, the pain wasn't nearly as bad for her. Instead, she was able to help biological mothers carry the pain of having to say goodbye to the children by volunteering for this.