Jill is the daughter of Kate and Luke, and traveled with them to the Gilead-American border to escape. However, they're caught by the police and Luke is shot, leaving Jill and Kate to be captured.
Jill is presumably sedated and then placed under the custody of her new family. We don't see much of her new life beyond a picture.
"Mommy!" -Jill, moments before capture
|Kate | Serena Joy | Nick | Moira | Aunt Lydia | Commander | Ofglen | Janine | Aunt Helena | Aunt Elizabeth | Luke | Cora | Aunt Sara | Rita | June | Dick | Alma | Aunt Christina | Mrs. Warren | Steve | Ofglen #2 | Jill|