M.F.
A stroller would help contain her, keep her safe and help you tote some of your stuff through the airport. You can gate-check it, so you'll have it with you the whole time. If she's restless in the stroller before the flight, you can just walk through the terminal pushing the stoller with one hand and holding her hand with the other. I have to say I'm not a fan of harnesses for children. Whatever they're called, they're still basically a leash for your kid, and I think interaction and a parent's hand does the same job in a much better way. Good luck!