Naps

My daughter is 4 months old and for the past month she wakes up after 30 minutes when taking her naps. Every single time! I typically just leave her in her crib for about 15 minutes and she will settle herself to go back to sleep for another 30 minutes. Any suggestions on how I can help her sleep for longer stretches during naps? I feel like 30 minutes isn’t a full restful sleep cycle.