Change in wake up time

My 15 month old was waking between 7:00-7:15 for the longest time. Three weeks ago she suddenly started waking between 6:00-6:30. She was still taking two naps and was going down fine for both naps. I thought the early wake ups may be a sign of needing to transition to 1 nap so we made the switch. She‘s now been on a 1 nap schedule for 2 weeks and is still waking between 6:00-6:30. Her schedule is:

6:00-6:30 wake up

12:00 nap (she typically wakes around 2)

8:15 bedtime

She is in a room with blackout curtains and a sound machine. The room is temperature controlled. No other changes have happened in her life recently. Any advice on how to get back to the 7:00 wake ups?? Thank you!