Theres nothing suspicious at all, this question tends to get asked often. Where does your friend often travel to and from where she is getting secondary screening? Did she have any issues with CBP when coming to the US? etc. More details will help give a clearer answer. A redress number is unlikely to help internationally and really only helps those who are often miss identified by the TSA's secure flight program.
Not being able to check in may be due to several different factors and may have been dependent on the airlines rules. For example her passport and or visa may have needed to be verified by the airline.