Hi there, I just wanted to add one more to your list LOL and that is cold, with the colder weather coming in you may find that she is cold. The 5am wake up is generally for this reason as it is when it is generally coldest for them. They wake every 40minutes because of their sleep cycles so if they wake and they are cold, they wake up more and then think it is time to get up for the day.

Try a sleeping bag and see if this helps.

The only other thing is that it could be that she is getting close to drop a day nap, and when this happens they start waking early for a couple of months and then start sleeping in again when the nap has been dropped.