D.D.
How is her day time mood? Is she whiny? Does she fuss a lot? Is she clingy with you? If so, then she is not getting the sleep she needs, and it may be sleep apnea. I suggest that you follow up with a pediatric ENT, since the regular pediatrician thinks all is okay. My friend's son was exactly like your daughter, and when they finally took all the adenoids and tonsils, he slept like a rock and his personality changed completely. Happy happy boy now!