She is not Invisible by Marcus Sedgwick

What's it all about?                                                                                                                                                                     Sixteen-year-old Laureth kidnaps her "slightly strange" little brother, Benjamin, and embarks on a transatlantic journey to New York to find her missing father, the famous author, Jack Peak. Laureth suspects that something terrible has happened after receiving an email from a Mr Michael Walker, saying that he has found her father's notebook in Queens - Jack is supposed to be in Switzerland.  Compelled by her mother's apparent lack of concern, Laureth hatches a plan to track down her father, convinced that he needs her help. It is only when Laureth and Benjamin arrive at the airport that we realise why she is 'abducting' her little brother: Laureth is blind and will need him to help her navigate around the unfamiliar territory of the airport and of New York.