I was just thinking about asking this yesterday. My SM has only been napping about every third day. But she NEEDS it every day. On the days she doesn't, I make her stay in her room for at least 45 minutes and play on her bed.
The other day, DH tried to put her down for a nap. He told her to have a "happy nappy," put up the gate at her door, and left. Five minutes later she was at the gate yelling, "Daddy! I had my happy nappy, and I'm sooooo HAPPY!!!!!!! He told her she couldn't possibly have taken a nap yet, and she replied, "But I'm fresh out of naps." LOL