L.L.
My daughter successfully sleeps in a play pen, but I had to pad it because it wasn't comfortable. I take three blankets and fold up over the pad, and then take a sheet designed for a playpen and tuck it around all of them to make it more cushy. This should be okay for your daughter, since she's older.
No advice on how to get her into it, other than to make sure she's asleep before you put her down. I know that's the opposite of what they tell you to do (put them down when they are awake? Ha!) but that's what works for me...I hold her after she's asleep for about ten minutes, and then transfer her over. Just take it slow and try to maintain as much body contact until she's down. Don't give in, and she will get used to it.