When I went from temp to perm at my previous job, my agency rep gave me a small, ceramic, heart shaped picture frame. It was to nice to keep at work, but it was perfect for my nightstand (I was actually scared I or someone else would knock it over and break it at work.) Because I had been out of work for a year and a half before that assignment it serves as a reminder to me of just how far I've come in my life the past 8 + years.
Does she have children, friends, family or a SO that she keeps a picture of on or near her desk? Something nice and professional looking may do the trick or even a nice print that she can hang in her office or at home. Its really hard to give suggestions when you don't know the person and their likes/dislikes. Shoot, its hard when you do.

Or how about if you and your boss both take her to lunch once he returns from the trip. That way she can find out first hand how much her help assisted him in having a smooth trip.
Just a thought or two.
Michelle
