There's one possible thing that they may be up against. If there was some type of government security issue that prevented her from traveling. Either a flight marshal needing a seat, triggering additional scrutiny by the government before she was cleared to fly, passport issues, etc . In those cases they're limited to not being able to say the real reason. I find it highly odd that they won't give the actual reason, that multiple agents refuse to give an actual answer.
Lastly no one accused your daughter of purposefully doing something or not disclosing relevant information. However you noted she was a mouse, and thus the question was did she didn't realize something was important to the story.