M.M.
It's GREAT that she can get herself back to sleep. I would not worry at all. Her diapers shouldn't be an issue either. If she was uncomfortable she'd let you know.
One thing I noticed with my son (who is 3) is giving him his vitamins at dinner made it harder for him to stay asleep. When I give him vitamins in the morning, he is good at night. When I give them to him later, he is more keyed up throughout the night. I don't know if there's any scientific basis to that... it's just something I played around with.