You can't go past security with her unless she is an unaccompanied minor
Yes
Yes you can wait with her.
reach out to the airline and ask them the policy. How Do I Get an Escort Pass? It is usually easy to get an escort pass. Simply go with your relative or friend to the check-in counter, request a pass, and present your photo ID. You can call ahead to get escort pass information, but you will probably be told that issuance of escort passes is determined locally by each airline. there is a mobile app called My TSA. You could ask there for your specific airport.
Depending on her age. If she wants s under 15 then yes. You can get a pass so you can wait at the gate with her. If she is over 15 then no. I had to do this with my step children for many years.
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