Our 13 year old son and 14 year old nephew have both flown alone recently and didn't need an id of any kind. At the check-in counter, you can request to accompany your daughter to her gate and they will print you a non-boarding pass. They will request an id from you before printing the pass and you will be asked to show it again at security. Southwest allowed myself and my husband to accompany our son to his gate. And they also allowed my husband and I, as well as our son, to accompany our nephew to his gate. Both instances we stayed with him until he boarded and the plane left.