E.L.
My daughter who is 15 months old has gone through phases like this at her nap times. At first I would go in often like every ten minutes. But she knew I would be in a short amount of time. Then I would wait 20 minutes to go in the first time, then 30 minutes the second time, and then she would go to sleep after the second time. After only one day of doing it like this she no longer had difficulty going to sleep on her own initially. Hope that helps.