Get to the airport early and talk to the ticket counter. Since she is a minor they will likely give you a pass to go through security and meet her. If you have status with the airline even better.
A few months back our 25 year old was traveling through IAH out of the country. Hubby has a membership to the United Lounge, they told us to just say we were going there. They gave us a pass we went through security, had lunch with son, gave him some things he needed and he gave us the things he needed us to keep for him.
Just make sure you emphasize that your afraid she'll get confused or overwhelmed.
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