I'm not sure who to call or what to google (the airlines or the airport?) Is this even allowed any more?
DD#2 is going to France in a couple of months and she wants me to come inside the airport and wait with her until she boards the plane. I'd really like to do that, and I'd like to meet her at the arrival gate when she gets off the plane coming back home.
I am under the impression that you need to have a ticket in order to get past the security check-in. Is this true?
How do I find out what I need to do so that I can wait with her before departure and meet her once she arrives?
I think I would first check the TSA website, or if there's a specific page of TSA requirements on the airport website. You (and DD2) should get familiar with this information so she knows what she can pack, what can be carried on, plus how and when to check in for an international flight (even if she has a leg within the U.S.). DD2 will also have to know what to do at customs in France.
In my experience, you need a boarding pass to get past security, and there is a passenger meeting area after landing. However, there's nothing to lose by calling the airport and asking.
The best you probably can do is to have a nice meal with her before she goes through the security.