My daughter will be flying in to Rome at 7:00 p.m., we have 9:00 dinner reservations at Armando, and we'd hope she can get to join us. If we arrange a cab to pick her up, is an hour enough time?
Once she's sitting on the taxi, she'll be there in 40-45 min max.
The issue is whether the airplane arrives on time, and whether the arrival procedures go smoothly and quickly (deplane, passport control if she arrives from outside Schengen, and, above all, baggage claim).
With 9:00 reservations you'll have the table until they close. Your daughter can join you at the restaurant when she arrives.
Wait, two hours to get from FCO to a restaurant in Rome? I doubt that will happen. The Leonardo Express takes 30 minutes and once you allow for the time to get off the plane and walk quite a distance just to get to the train you have used up another 15 - 30 minutes. This does not even allow for time to gather bags, if they were checked, or get through passport control if she is arriving from outside of the schengen area.