Melissa Hartswell is the mother of Jennifer Hartswell, a girl with very high immune response that the Visitors want to harvest DNA from. As such, they plan for Melissa to be a member of the live-aboards. Melissa is reticent about moving to the Mothership for fear of having to leave Jennifer behind.
Anna arranges to meet Melissa and explains to her that Jennifer can also live on board the Mothership with Melissa, but Melissa is concerned that there are no children aboard. To that, Anna tells Melissa that she actually has a child exactly the same age as Jennifer, by the name of Amy (which happens to be Melissa's mother's name).
After hearing about a potential play-mate for Jennifer, Melissa relents and agrees to live aboard the Mothership, especially when Jennifer expresses excitement in meeting Amy.