Sleeping on her tummy...
For Hadley's mid-day nap, I laid her down in her play-yard (aka playpen) and she whimpered for about 2 minutes and then was quiet. About a minute later I checked on her and she was mostly sleeping. Eyes closed - thumb in mouth. ON HER TUMMY. I thought I would leave her as this would be a good supervised trial of how she reacted through sleeping and wake up. She was fine.
I will still put her to sleep on her back but hopefully these supervised practice rounds will help her if she rolls while I am sleeping at night.