Hi there, your easy looks pretty good to be honest. Long wakings at that time of night were always either UT or discomfort or developmental change for us. I would think UT is unlikely as she's only just moved to one nap.
Teething is a possibility, have you tried offering medicine as she wakes, or just before (say at your BT) as a dreamfeed. She might not appear to be in pain but just be slightly too uncomfortable to go back to sleep.
If it's not UT or teething then is there anything going on for her in the day at the moment, is she learning anything new?