The connection in Atlanta will not be specially complicated. First your daughter will have a long walk to Immigration. There will be two separate lines, one for US citizens and residents and another one for visiting foreigners. After that she will go down one level, retrieve her baggage and clear Customs. After exiting Customs she will be directed to drop off her bags for the next flight. Next she will check the departures board to see from which gate her flight will be leaving. She will then go down one more level to the train that will take her to the appropriate concourse and her gate. Signage is clear and she can always ask someone for directions if necessary. There should be plenty of time for all this unless the flight from Chile is quite late.