What does a 13 year old need to bring to the airport when traveling alone? [closed]

She'll need the same documents as anyone else. In Europe an ID will be okay, outside Europe she will need her local identification (passport, ID, ..., what is used in your country). Using her identification and her ticket, she will be able to get her boarding pass, which is used to go through security and to board the plane. She will have to go through the exact same procedure (cabin bag check etc.). Please consult your airline.

I know many airlines who accompany minors, in this case they have to report to an info desk, and an airline representative will accompany them through check-in, security, to the gate. Another airline representative waits at the gate when they land, and accompanies them from the airplane to baggage claim to arrivals. Once at arrivals, they will only release the minor to someone who identifies himself/herself as the person who will be responsible for pickup (this is communicated to the airline in advance).

Please check this with your airline. If they have this service, they will also provide you a list with everything she'll need.

Edit: taken Calchas comment into account, thanks for the correction